automatic link-local address configuration:
- Convert a sysctl net.inet6.ip6.accept_rtadv to one for the
default value of a per-IF flag ND6_IFF_ACCEPT_RTADV, not a
global knob. The default value of the sysctl is 0.
- Add a new per-IF flag ND6_IFF_AUTO_LINKLOCAL and convert a
sysctl net.inet6.ip6.auto_linklocal to one for its default
value. The default value of the sysctl is 1.
- Make ND6_IFF_IFDISABLED more robust. It can be used to disable
IPv6 functionality of an interface now.
- Receiving RA is allowed if ip6_forwarding==0 *and*
ND6_IFF_ACCEPT_RTADV is set on that interface. The former
condition will be revisited later to support a "host + router" box
like IPv6 CPE router. The current behavior is compatible with
the older releases of FreeBSD.
- The ifconfig(8) now supports these ND6 flags as well as "nud",
"prefer_source", and "disabled" in ndp(8). The ndp(8) now
supports "auto_linklocal".
Discussed with: bz and jinmei
Reviewed by: bz
MFC after: 3 days
2eb62239d7