MFC r313025, r313395, r314113, r314442, r315458, r315656

r313025:
Add tests for multi-fib IPv6 routing

PR: 196361
Submitted by: jhujhiti@adjectivism.org
Reported by: Jason Healy <jhealy@logn.net>
MFC after: 4 weeks
Sponsored by: Spectra Logic Corp

r313395:
Add fibs_test:udp_dontroute6, another IPv6 multi-FIB test

PR: 196361
MFC after: 3 weeks
Sponsored by: Spectra Logic Corp

r314113:
Remove tests/sys/netinet/fibs_tests's dependency on net/socat

Instead of bridging two tap interfaces with socat, just use an epair pair.

MFC after: 3 weeks
Sponsored by: Spectra Logic Corp

r314442:
Add an ATF test for IPv6 SLAAC with multiple fibs

Tests that an interface can get a SLAAC address and that it inserts its
routes into the correct fib. Does not test anything to do with NDP.

PR: 196361
Reviewed by: Erick Turnquist <jhujhiti@adjectivism.org>
MFC after: 3 weeks
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D9776

r315458:
Constrain IPv6 routes to single FIBs when net.add_addr_allfibs=0

sys/netinet6/icmp6.c
Use the interface's FIB for source address selection in ICMPv6 error
responses.

sys/netinet6/in6.c
In in6_newaddrmsg, announce arrival of local addresses on the
interface's FIB only. In in6_lltable_rtcheck, use a per-fib ND6
cache instead of a single cache.

sys/netinet6/in6_src.c
In in6_selectsrc, use the caller's fib instead of the default fib.
In in6_selectsrc_socket, remove a superfluous check.

sys/netinet6/nd6.c
In nd6_lle_event, use the interface's fib for routing socket
messages. In nd6_is_new_addr_neighbor, check all FIBs when trying
to determine whether an address is a neighbor. Also, simplify the
code for point to point interfaces.

sys/netinet6/nd6.h
sys/netinet6/nd6.c
sys/netinet6/nd6_rtr.c
Make defrouter_select fib-aware, and make all of its callers pass in
the interface fib.

sys/netinet6/nd6_nbr.c
When inputting a Neighbor Solicitation packet, consider the
interface fib instead of the default fib for DAD. Output NS and
Neighbor Advertisement packets on the correct fib.

sys/netinet6/nd6_rtr.c
Allow installing the same host route on different interfaces in
different FIBs. If rt_add_addr_allfibs=0, only install or delete
the prefix route on the interface fib.

tests/sys/netinet/fibs_test.sh
Clear some expected failures, but add a skip for the newly revealed
BUG217871.

PR: 196361
Submitted by: Erick Turnquist <jhujhiti@adjectivism.org>
Reported by: Jason Healy <jhealy@logn.net>
Reviewed by: asomers
MFC after: 3 weeks
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D9451

r315656:
Fix back-to-back runs of sys/netinet/fibs_test;slaac_on_nondefault_fib6

This test was failing if run twice because rtadvd takes too long to die.
The rtadvd process from the first run was still running when the
second run created its interfaces. The solution is to use SIGKILL during
the cleanup instead of SIGTERM so rtadvd will die faster.

While I'm here, randomize the addresses used for the test, which makes bugs
like this easier to spot, and fix the cleanup order to be the opposite of
the setup order

PR: 217871
MFC after: 18 days
X-MFC-With: 315458
Sponsored by: Spectra Logic Corp