MFC r264887

Fix host and network routes for new interfaces when net.add_addr_allfibs=0

sys/net/route.c
        In rtinit1, use the interface fib instead of the process fib.  The
        latter wasn't very useful because ifconfig(8) is usually invoked
        with the default process fib.  Changing ifconfig(8) to use setfib(2)
        would be redundant, because it already sets the interface fib.

tests/sys/netinet/fibs_test.sh
        Clear the expected ATF failure

sys/net/if.c
        Pass the interface fib in calls to rtrequest1_fib and rtalloc1_fib

sys/netinet/in.c
sys/net/if_var.h
        Add a fibnum argument to ifa_switch_loopback_route, a subroutine of
        in_scrubprefix.  Pass it the interface fib.
MFC changes related to PR kern/189089.  Unlike CURRENT, stable/10 does not
panic when you attempt to remove the IP address.  But it still fails to
remove the address.

MFC r265094

Add regression test for PR kern/189088.

MFC r265092

Fix a panic when removing an IP address from an interface, if the same
address exists on another interface.  The panic was introduced by change
264887, which changed the fibnum parameter in the call to rtalloc1_fib() in
ifa_switch_loopback_route() from RT_DEFAULT_FIB to RT_ALL_FIBS.  The
solution is to use the interface fib in that call.  For the majority of
users, that will be equivalent to the legacy behavior.