checksum offloading and VLAN hardware tag insertion/stripping from
the currently enabled hardware offloading capabilities.
Previously if_hwassist, which was initialized to TX/RX checksum
offloading, was blindly used to enable both TX and RX checksum
offloading such that disabling either TX or RX checksum offloading
was not possible.
ti(4) controllers support TX/RX checksum offloading with VLAN
tagging so announce TX/RX checksum offloading capability over VLAN
to vlan(4).
Make VLAN hardware tag insertion/stripping honors currently enabled
interface capability instead of blindly enabling VLAN hardware
tagging. This change allows disabling hardware support of VLAN tag.
Because ti(4) supports VLAN oversized frames, make network stack
know the capability by setting if_hdrlen.
While I'm here, rewrite SIOCSIFCAP handler and make sure to
reinitialize controller whenever TX/RX checksum offloading and VLAN
hardware tagging option is changed. The requirement of controller
reinitialization comes from the limitation of Tigon I/II firmware.
Tigon I/II firmware requires all related RCBs should be
reinitialized whenever any of its hardware offloading capabilities
change.
vlan(4) is also notified whenever the parent interface's capability
changes such that it can correctly handle TX/RX checksum offloading
based on parent interface's enabled offloading capabilities.
RX checksum offloading handler was changed to make upper stack use
controller computed partial checksum value. Previously, ti(4) just
set the computed value for any frames(IPv4, IPv6) and the value was
not used in upper stack because driver didn't set CSUM_DATA_VALID
such that upper network stack had to recompute checksum of TCP/UDP
packets. I have no idea how this was not noticed for a long time.
With this change, upper network stack does not have to fully
recompute the checksum such that calculating pseudo checksum based
on partial checksum is sufficient to know whether received packet's
checksum is correct or not. However, I don't know why ti(4) does
not have controller compute pseudo checksum as controller has
ability to do it. I'm just guessing enabling that feature could
trigger a firmware bug or could be slower than computing it on host
side so just leave it as it was.
In order not to produce false positives, ti(4) now checks whether
controller actually computed IP or TCP/UDP checksum by checking
ti_flags field.
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