MFC r263445 and r265385.  Note that the change to ObsoleteFiles.inc in
r265385 does not need to be MFCed, because the obsolete files in question
were never MFCed to any stable branch.

r265385
Remove the ifconfig test added in rev 263445.  After discussion with
melifaro, we agreed that ifconfig's behavior was not a bug.  The main
motivation for bin/187551 was to partially resolve kern/187549, but we
resolved kern/187549 in a different way instead.

ObsoleteFiles.inc
etc/mtree/BSD.tests.dist
sbin/ifconfig/tests/fibs_test.sh
sbin/ifconfig/tests/Makefile
sbin/ifconfig/Makefile
        Remove /usr/tests/sbin/ifconfig

r263445
Add several ATF tests that deal with multiple fibs.  They're described in
several different PRs, but the tests share some common code, so I'm
committing them together.

sbin/ifconfig/tests
sbin/ifconfig/tests/fibs_test.sh
sbin/ifconfig/tests/Makefile
sbin/ifconfig/Makefile
        Add fibs_test.sh, which regresses bin/187551

tests/sys/netinet
tests/sys/netinet/fibs_test.sh
tests/sys/netinet/udp_dontroute.c
tests/sys/netinet/Makefile
tests/sys/Makefile
        Add fibs_test.sh, which regresses kern/167947, kern/187552
        kern/187549, kern/187550, and kern/187553

etc/mtree/BSD.tests.dist
        Add newly created directories