Commit Graph

4560 Commits

Author SHA1 Message Date
Alexander V. Chernikov
adc4ea97bd Turn off forgotten multipath debug messages
Reported by:	mike tancsa<mike at sentex.net>
MFC after:	3 days
2021-02-08 21:42:20 +00:00
Alexander V. Chernikov
4a01b854ca SO_RERROR indicates that receive buffer overflows should be handled as errors.
Historically receive buffer overflows have been ignored and programs
could not tell if they missed messages or messages had been truncated
because of overflows. Since programs historically do not expect to get
receive overflow errors, this behavior is not the default.

This is really really important for programs that use route(4) to keep in sync
with the system. If we loose a message then we need to reload the full system
state, otherwise the behaviour from that point is undefined and can lead
to chasing bogus bug reports.
2021-02-08 21:42:20 +00:00
Alexander V. Chernikov
eb0b1b33d5 Enable multipath routing by default.
ROUTE_MPATH was added to the GENERIC kernel in r368648.

According to the plan in D27428, it was enabled with `net.route.multipath` sysctl set to 0.
Given enough time has passed, this change enables route multipath by default.

The goal is to ship FreeBSD 13 with multipath turned on.

Reviewed By: donner, olivier
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D28423
2021-02-03 08:49:58 +00:00
Sai Rajesh Tallamraju
38bfc6dee3 iflib: Free resources in a consistent order during detach
Memory and PCI resources are freed with no particular order.  This could
cause use-after-frees when detaching following a failed attach.  For
instance, iflib_tx_structures_free() frees ctx->ifc_txqs[] but
iflib_tqg_detach() attempts to access this array. Similarly, adapter
queues gets freed by IFDI_QUEUES_FREE() but IFDI_DETACH() attempts to
access adapter queues to free PCI resources.

MFC after:	2 weeks
Sponsored by:	NetApp, Inc.
Differential Revision:	https://reviews.freebsd.org/D27634
2021-02-01 11:15:54 -05:00
Jonah Caplan
88be0e1120 bridge: fix STP roles and protos strings
Add the missing commas that got lost in e5539fb618.

PR:		252532
Reviewd by:	kp@, donner@, freqlabs@
MFC after:	3 days
Differential Revision:	https://reviews.freebsd.org/D28425
2021-02-01 15:27:06 +01:00
Alexander V. Chernikov
78c93a1721 Use process fib for inet/inet6 fib_algo sysctls.
This allows to set/query fib algo for non-default fibs.

MFC after:	3 days
2021-01-31 10:50:08 +00:00
Alexander V. Chernikov
151ec796a2 Fix the design problem with delayed algorithm sync.
Currently, if the immutable algorithm like bsearch or radix_lockless
 receives rtable update notification, it schedules algorithm rebuild.
This rebuild is executed by the callout after ~50 milliseconds.

It is possible that a script adding an interface address and than route
 with the gateway bound to that address will fail. It can happen due
 to the fact that fib is not updated by the time the route addition
 request arrives.

Fix this by allowing synchronous algorithm rebuilds based on certain
 conditions. By default, these conditions assume:
1) less than net.route.algo.fib_sync_limit=100 routes
2) routes without gateway.

* Move algo instance build entirely under rib WLOCK.
 Rib lock is only used for control plane (except radix algo, but there
  are no rebuilds).
* Add rib_walk_ext_locked() function to allow RIB iteration with
 rib lock already held.
* Fix rare potential callout use-after-free for fds by binding fd
 callout to the relevant rib rmlock. In that case, callout_stop()
 under rib WLOCK guarantees no callout will be executed afterwards.

MFC after:	3 days
2021-01-30 23:25:57 +00:00
Alexander V. Chernikov
dd9163003c Add rib_subscribe_locked() and rib_unsubsribe_locked() to support
subscriptions during RIB modifications.
Add new subscriptions to the beginning of the lists instead of
 the end. This fixes the situation when new subscription is created
 int the callback for the existing subscription, leading to the
 subscription notification handler pick it.

MFC after: 3 days
2021-01-30 23:25:57 +00:00
Alexander V. Chernikov
ab6d9aaed7 Move business logic from rebuild_fd_callout() into rebuild_fd().
This simplifies code a bit and allows for future non-callout
 callers to request rebuild.

MFC after:	3 days
2021-01-30 23:25:57 +00:00
Alexander V. Chernikov
f8b7ebea49 Improve fib_algo debug messages.
* Move per-prefix debug lines under LOG_DEBUG2
* Create fib instance counter to distingush log messages between
 instances
* Add more messages on rebuild reason.

MFC after:	3 days
2021-01-30 23:25:56 +00:00
Alexander V. Chernikov
cb984c62d7 Fix multipath support for rib_lookup_info().
The initial plan was to remove rib_lookup_info() before
 FreeBSD 13. As several customers are still remaining,
 fix rib_lookup_info() for the multipath use case.
2021-01-29 23:14:24 +00:00
Alexander V. Chernikov
53729367d3 Fix subinterface vlan creation.
D26436 introduced support for stacked vlans that changed the way vlans
 are configured.  In particular, this change broke setups that have
 same-number vlans as subinterfaces.

Vlan support was initially created assuming "vlanX" semantics. In this paradigm,
 automatic number assignment supported by cloning (ifconfig vlan create) was a
 natural fit.
When "ifaceX.Y" support was added, allowing to have the same vlan number on
 multiple devices, cloning code became more complex, as the is no
unified "vlan" namespace anymore. Such interfaces got the first spare
index from "vlan" cloner. This, in turn, led to the following problem:
 ifconfig ix0.333 create -> index 1
 ifconfig ix0.444 create -> index 2
 ifconfig vlan2 create -> allocation failure

This change fixes such allocations by using cloning indexes only for
 "vlanX" interfaces.

Reviewed by:            hselasky
MFC after:		3 days
Differential Revision:  https://reviews.freebsd.org/D27505
2021-01-29 21:43:20 +00:00
Gleb Smirnoff
3f43ada98c Catch up with 6edfd179c8: mechanically rename IFCAP_NOMAP to IFCAP_MEXTPG.
Originally IFCAP_NOMAP meant that the mbuf has external storage pointer
that points to unmapped address.  Then, this was extended to array of
such pointers.  Then, such mbufs were augmented with header/trailer.
Basically, extended mbufs are extended, and set of features is subject
to change.  The new name should be generic enough to avoid further
renaming.
2021-01-29 11:46:24 -08:00
Randall Stewart
1a714ff204 This pulls over all the changes that are in the netflix
tree that fix the ratelimit code. There were several bugs
in tcp_ratelimit itself and we needed further work to support
the multiple tag format coming for the joint TLS and Ratelimit dances.

    Sponsored by: Netflix Inc.
    Differential Revision:  https://reviews.freebsd.org/D28357
2021-01-28 11:53:05 -05:00
Kristof Provost
35dabb7b9c altq: Fix typo in features sysctl description
Reported by:	Jose Luis Duran
2021-01-27 16:42:14 +01:00
Kristof Provost
27b2aa4938 altq: Remove unused arguments from altq_attach()
Minor cleanup, no functional change.

Reviewed by:		donner@
Differential Revision:	https://reviews.freebsd.org/D28304
2021-01-25 19:58:22 +01:00
Kristof Provost
e111d79806 Add FEATURE sysctls for ALTQ disciplines
This will allow userspace to more easily figure out if ALTQ is built
into the kernel and what disciplines are supported.

Reviewed by:		donner@
Differential Revision:	https://reviews.freebsd.org/D28302
2021-01-25 19:58:22 +01:00
Vincenzo Maffione
f80efe5016 iflib: netmap: move per-packet operation out of fragments loop
MFC after:	1 week
2021-01-24 21:38:59 +00:00
Vincenzo Maffione
aceaccab65 iflib: netmap: add support for NS_MOREFRAG
The NS_MOREFRAG flag can be set in a netmap slot to represent a
multi-fragment packet. Only the last fragment of a packet does
not have the flag set. On TX rings, the flag may be set by the
userspace application. The kernel will look at the flag and use it
to properly set up the NIC TX descriptors.
On RX rings, the kernel may set the flag if the packet received
was split across multiple netmap buffers. The userspace application
should look at the flag to know when the packet is complete.

Submitted by:	rajesh1.kumar_amd.com
Reviewed by:	vmaffione
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D27799
2021-01-24 21:20:59 +00:00
Andrew Gallatin
0c864213ef iflib: Fix a NULL pointer deref
rxd_frag_to_sd() have pf_rv parameter as NULL with the current
code. This patch fixes the NULL pointer dereference in that
case thus avoiding a possible panic.

Submitted by: rajesh1.kumar at amd.com
Reviewed by: gallatin
Differential Revision: https://reviews.freebsd.org/D28115
2021-01-21 09:47:06 -05:00
Alexander V. Chernikov
9d6567bc30 Fix panic on vnet creation if fib algo has been set to fixed value.
Make fixed algo property per-VNET instead of global.
2021-01-17 20:32:25 +00:00
Alexander V. Chernikov
f9e0752e35 Create new in6_purgeifaddr() which purges bound ifa prefix if
it gets unused.

Currently if_purgeifaddrs() uses in6_purgeaddr() to remove IPv6
 ifaddrs. in6_purgeaddr() does not trrigger prefix removal if
 number of linked ifas goes to 0, as this is a low-level function.
 As a result, if_purgeifaddrs() purges all IPv4/IPv6 addresses but
 keeps corresponding IPv6 prefixes.

Fix this by creating higher-level wrapper which handles unused
 prefix usecase and use it in if_purgeifaddrs().

Differential revision:	https://reviews.freebsd.org/D28128
2021-01-17 20:32:25 +00:00
Alexander V. Chernikov
81728a538d Split rtinit() into multiple functions.
rtinit[1]() is a function used to add or remove interface address prefix routes,
  similar to ifa_maintain_loopback_route().
It was intended to be family-agnostic. There is a problem with this approach
 in reality.

1) IPv6 code does not use it for the ifa routes. There is a separate layer,
  nd6_prelist_(), providing interface for maintaining interface routes. Its part,
  responsible for the actual route table interaction, mimics rtenty() code.

2) rtinit tries to combine multiple actions in the same function: constructing
  proper route attributes and handling iterations over multiple fibs, for the
  non-zero net.add_addr_allfibs use case. It notably increases the code complexity.

3) dstaddr handling. flags parameter re-uses RTF_ flags. As there is no special flag
 for p2p connections, host routes and p2p routes are handled in the same way.
 Additionally, mapping IFA flags to RTF flags makes the interface pretty messy.
 It make rtinit() to clash with ifa_mainain_loopback_route() for IPV4 interface
 aliases.

4) rtinit() is the last customer passing non-masked prefixes to rib_action(),
 complicating rib_action() implementation.

5) rtinit() coupled ifa announce/withdrawal notifications, producing "false positive"
 ifa messages in certain corner cases.

To address all these points, the following has been done:

* rtinit() has been split into multiple functions:
- Route attribute construction were moved to the per-address-family functions,
 dealing with (2), (3) and (4).
- funnction providing net.add_addr_allfibs handling and route rtsock notificaions
 is the new routing table inteface.
- rtsock ifa notificaion has been moved out as well. resulting set of funcion are only
 responsible for the actual route notifications.

Side effects:
* /32 alias does not result in interface routes (/32 route and "host" route)
* RTF_PINNED is now set for IPv6 prefixes corresponding to the interface addresses

Differential revision:	https://reviews.freebsd.org/D28186
2021-01-16 22:42:41 +00:00
Alexander V. Chernikov
a6b7689718 Remove redundant rtinit() calls from tuntap.
Removed code iterates over if_addrhead and tries to remove
 routes for each ifa.
This is exactly the thing that if_purgeaddrs() do, and
 if_purgeaddr() is already called in the end.

Reviewed by:		glebius
MFC after:		2 weeks
Differential revision:	https://reviews.freebsd.org/D28106
2021-01-13 10:03:15 +00:00
Ryan Libby
c86fa3b8d7 pf: quiet -Wredundant-decls for pf_get_ruleset_number
In e86bddea9f sys/netpfil/pf/pf.h grew a
declaration of pf_get_ruleset_number.  Now delete the old declaration
from sys/net/pfvar.h.

Reviewed by:	kp
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D28081
2021-01-10 21:53:15 -08:00
Alexander V. Chernikov
685de460bc Use static initializers for fib algo to shift initialization
to ealier stage. This allows to register modules loaded at
 boot time.

Reported by:	olivier
2021-01-11 00:16:54 +00:00
Vincenzo Maffione
55f0ad5fde netmap: restore hwofs and support it in iflib
Restore the hwofs functionality temporarily disabled by
7ba6ecf216 to prevent issues with iflib.
This patch brings the necessary changes to iflib to
enable howfs to allow interface restarts without
disrupting netmap applications actively using its
rings.
After this change, it becomes possible for multiple
non-cooperating netmap applications to use non-overlapping
subsets of the available netmap rings without clashing
with each other.

PR:		252453
MFC after:	1 week
2021-01-10 22:51:15 +00:00
Vincenzo Maffione
8aa8484cbf iflib: fix build failure in case DEV_NETMAP is not defined
This addresses the build failure introduced by
3d65fd97e8.

MFC with: 3d65fd97e8
2021-01-10 14:43:58 +00:00
Vincenzo Maffione
4ba9ad0dc3 iflib: add assert to prevent out-of-bounds array access
The iflib_queues_alloc() allocates isc_nrxqs iflib_dma_info structs
for each rxqset, and links each struct to a different free list.
As a result, it must be isc_nrxqs >= isc_nfl (plus the completion
queue, if present).
Add an assertion to make this constraint explicit.

MFC after:	2 weeks
2021-01-10 13:59:20 +00:00
Vincenzo Maffione
3d65fd97e8 netmap: iflib: enable/disable krings on any interface reinit
Since 1d238b07d5, krings are disabled before
a reinit cycle triggered by iflib_netmap_register.
However, this operation is actually necessary also for
any interface reinit triggered by other causes (i.e.,
ifconfig commands).
We achieve this goal by moving the krings enable/disable
operation inside iflib_stop() and iflib_init_locked().

Once here, this change also removes some redundant operations
from iflib_netmap_register(), that are already performed by
iflib_stop().

PR:		252453
MFC after:	1 week
2021-01-10 12:04:08 +00:00
Vincenzo Maffione
3189ba6167 netmap: iflib: fix asserts in netmap_fl_refill()
When netmap_fl_refill() is called at initialization time (e.g.,
during netmap_iflib_register()), nic_i must be 0, since the
free list is reinitialized. At the end of the refill cycle, nic_i
must still be zero, because exactly N descriptors (N is the ring size)
are refilled.
This patch therefore fixes the assertions to check on nic_i rather
than on nm_i. The current netmap_reset() may in fact cause nm_i
to be != 0 while the device is resetting: this may happen when
multiple non-cooperating processes open different subsets of the
available netmap rings.

PR:	    252518
MFC after:  1 week
2021-01-09 21:35:07 +00:00
Vincenzo Maffione
1d238b07d5 netmap: iflib: stop krings during interface reset
When different processes open separate subsets of the
available rings of a same netmap interface, a device
reset may be performed while one of the processes
is actively using some rings (e.g., caused by another
process executing a nmport_open()).
With this patch, such situation will cause the
active process to get a POLLERR, so that it can
have a chance to detect the situation.
We also guarantee that no process is running a txsync
or rxsync (ioctl or poll) while an iflib device reset
is in progress.

PR:	    252453
MFC after:  1 week
2021-01-09 21:01:46 +00:00
Matt Macy
81be655266 iflib: ensure that tx interrupts enabled and cleanups
Doing a 'dd' over iscsi will reliably cause stalls. Tx
cleaning _should_ reliably happen as data is sent.
However, currently if the transmit queue fills it will
wait until the iflib timer (hz/2) runs.

This change causes the the tx taskq thread to be run
if there are completed descriptors.

While here:

- make timer interrupt delay a sysctl

- simplify txd_db_check handling

- comment on INTR types

Background on the change:

Initially doorbell updates were minimized by only writing to the register
on every fourth packet. If txq_drain would return without writing to the
doorbell it scheduled a callout on the next tick to do the doorbell write
to ensure that the write otherwise happened "soon". At that time a sysctl
was added for users to avoid the potential added latency by simply writing
to the doorbell register on every packet. This worked perfectly well for
e1000 and ixgbe ... and appeared to work well on ixl. However, as it
turned out there was a race to this approach that would lockup the ixl MAC.
It was possible for a lower producer index to be written after a higher one.
On e1000 and ixgbe this was harmless - on ixl it was fatal. My initial
response was to add a lock around doorbell writes - fixing the problem but
adding an unacceptable amount of lock contention.

The next iteration was to use transmit interrupts to drive delayed doorbell
writes. If there were no packets in the queue all doorbell writes would be
immediate as the queue started to fill up we could delay doorbell writes
further and further. At the start of drain if we've cleaned any packets we
know we've moved the state machine along and we write the doorbell (an
obvious missing optimization was to skip that doorbell write if db_pending
is zero). This change required that tx interrupts be scheduled periodically
as opposed to just when the hardware txq was full. However, that just leads
to our next problem.

Initially dedicated msix vectors were used for both tx and rx. However, it
was often possible to use up all available vectors before we set up all the
queues we wanted. By having rx and tx share a vector for a given queue we
could halve the number of vectors used by a given configuration. The problem
here is that with this change only e1000 passed the necessary value to have
the fast interrupt drive tx when appropriate.

Reported by: mav@
Tested by: mav@
Reviewed by:    gallatin@
MFC after:      1 month
Sponsored by:   iXsystems
Differential Revision:  https://reviews.freebsd.org/D27683
2021-01-07 14:07:35 -08:00
Alexander V. Chernikov
d68cf57b7f Refactor rt_addrmsg() and rt_routemsg().
Summary:
* Refactor rt_addrmsg(): make V_rt_add_addr_allfibs decision locally.
* Fix rt_routemsg() and multipath by accepting nexthop instead of interface pointer.
* Refactor rtsock_routemsg(): avoid accessing rtentry fields directly.
* Simplify in_addprefix() by moving prefix search to a separate  function.

Reviewers: #network

Subscribers: imp, ae, bz

Differential Revision: https://reviews.freebsd.org/D28011
2021-01-07 19:38:19 +00:00
Kristof Provost
5a3b9507d7 pf: Convert pfi_kkif to use counter_u64
Improve caching behaviour by using counter_u64 rather than variables
shared between cores.

The result of converting all counters to counter(9) (i.e. this full
patch series) is a significant improvement in throughput. As tested by
olivier@, on Intel Xeon E5-2697Av4 (16Cores, 32 threads) hardware with
Mellanox ConnectX-4 MCX416A-CCAT (100GBase-SR4) nics we see:

x FreeBSD 20201223: inet packets-per-second
+ FreeBSD 20201223 with pf patches: inet packets-per-second
+--------------------------------------------------------------------------+
|                                                                        + |
| xx                                                                     + |
|xxx                                                                    +++|
||A|                                                                       |
|                                                                       |A||
+--------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x   5       9216962       9526356       9343902     9371057.6     116720.36
+   5      19427190      19698400      19502922      19546509     109084.92
Difference at 95.0% confidence
        1.01755e+07 +/- 164756
        108.584% +/- 2.9359%
        (Student's t, pooled s = 112967)

Reviewed by:	philip
MFC after:	2 weeks
Sponsored by:	Orange Business Services
Differential Revision:	https://reviews.freebsd.org/D27763
2021-01-05 23:35:37 +01:00
Kristof Provost
26c841e2a4 pf: Allocate and free pfi_kkif in separate functions
Factor out allocating and freeing pfi_kkif structures. This will be
useful when we change the counters to be counter_u64, so we don't have
to deal with that complexity in the multiple locations where we allocate
pfi_kkif structures.

No functional change.

MFC after:	2 weeks
Sponsored by:	Orange Business Services
Differential Revision:	https://reviews.freebsd.org/D27762
2021-01-05 23:35:37 +01:00
Kristof Provost
320c11165b pf: Split pfi_kif into a user and kernel space structure
No functional change.

MFC after:	2 weeks
Sponsored by:	Orange Business Services
Differential Revision:	https://reviews.freebsd.org/D27761
2021-01-05 23:35:37 +01:00
Kristof Provost
c3adacdad4 pf: Change pf_krule counters to use counter_u64
This improves the cache behaviour of pf and results in improved
throughput.

MFC after:	2 weeks
Sponsored by:	Orange Business Services
Differential Revision:	https://reviews.freebsd.org/D27760
2021-01-05 23:35:37 +01:00
Kristof Provost
c7bdafe2f1 pf: Remove unused fields from pf_krule
The u_* counters are used only to communicate with userspace, as
userspace cannot use counter_u64. As pf_krule is not passed to userspace
these fields are now obsolete.

MFC after:	2 weeks
Sponsored by:	Orange Business Services
Differential Revision:	https://reviews.freebsd.org/D27759
2021-01-05 23:35:36 +01:00
Kristof Provost
e86bddea9f pf: Split pf_rule into kernel and user space versions
No functional change intended.

MFC after:	2 weeks
Sponsored by:	Orange Business Services
Differential Revision:	https://reviews.freebsd.org/D27758
2021-01-05 23:35:36 +01:00
Kristof Provost
dc865dae89 pf: Migrate pf_rule and related structs to pf.h
As part of the split between user and kernel mode structures we're
moving all user space usable definitions into pf.h.

No functional change intended.

MFC after:      2 weeks
Sponsored by:   Orange Business Services
Differential Revision:	https://reviews.freebsd.org/D27757
2021-01-05 23:35:36 +01:00
Kristof Provost
fbbf270eef pf: Use counter_u64 in pf_src_node
Reviewd by:	philip
MFC after:      2 weeks
Sponsored by:   Orange Business Services
Differential Revision:	https://reviews.freebsd.org/D27756
2021-01-05 23:35:36 +01:00
Kristof Provost
17ad7334ca pf: Split pf_src_node into a kernel and userspace struct
Introduce a kernel version of struct pf_src_node (pf_ksrc_node).

This will allow us to improve the in-kernel data structure without
breaking userspace compatibility.

Reviewed by:	philip
MFC after:	2 weeks
Sponsored by:	Orange Business Services
Differential Revision:	https://reviews.freebsd.org/D27707
2021-01-05 23:35:36 +01:00
Alexander V. Chernikov
9c0ff6a8bb Remove now-unused RT_GATEWAY* definitions.
They were used to simplify nexthop transition, hence not needed
 anymore.
2021-01-04 21:45:46 +00:00
Hans Petter Selasky
747feea146 Streamline the infiniband code according to the ethernet code.
Fix LINT-NOIP kernel build.

Submitted by:	rlibby @
Differential Revision:	https://reviews.freebsd.org/D27861
MFC after:	1 week
Sponsored by:	Mellanox Technologies // NVIDIA Networking
2020-12-31 10:07:02 +01:00
Hans Petter Selasky
ec52ff6d14 Streamline the infiniband code according to the ethernet code.
Specifically implement the if_requestencap callback function for infiniband.
Most of the changes are simply a cut and paste of the equivalent ethernet part.

Reviewed by:	melifaro @
Differential Revision:	https://reviews.freebsd.org/D27631
MFC after:	1 week
Sponsored by:	Mellanox Technologies // NVIDIA Networking
2020-12-29 18:01:57 +01:00
Hans Petter Selasky
19ecb5e8da Fix for IPoIB over lagg(4).
Need to update both link layer address and broadcast address when active link changes for IP over infiniband.
This is because the broadcast address contains the so-called P-key, which is interface dependent.

Reviewed by:	kib @
Differential Revision:	https://reviews.freebsd.org/D27658
MFC after:	1 week
Sponsored by:	Mellanox Technologies // NVIDIA Networking
2020-12-29 17:35:06 +01:00
Ryan Libby
833dbf1e22 route: quiet -Wredundant-decls
Remove declaration duplicated in
f5baf8bb12

Reviewed by:	melifaro
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D27790
2020-12-27 16:32:27 -08:00
Alexander V. Chernikov
f733d9701b Fix default route handling in radix4_lockless algo.
Improve nexthop debugging.

Reported by:	Florian Smeets <flo at smeets.xyz>
2020-12-26 22:51:02 +00:00
Alexander V. Chernikov
4e19e0d92a Use light-weight versions of routing lookup functions in ng_netflow.
Use recently-added combination of `fib[46]_lookup_rt()` which
 returns rtentry & raw nexthop with `rt_get_inet[6]_plen()` which
 returns address/prefix length of prefix inside `rt`.

Add `nhop_select_func()` wrapper around inlined `nhop_select()` to
 allow callers external to the routing subsystem select the proper
 nexthop from the multipath group without including internal headers.

New calls does not require reference counting objects and reduce
 the amount of copied/processed rtentry data.

Differential Revision: https://reviews.freebsd.org/D27675
2020-12-26 11:27:38 +00:00