ifconfig: Exit with a non-zero status when SIOCSIFFIB failsHEADmain

Previously, setting an interface FIB to some invalid value would result
in a warning being printed, but the ifconfig command would exit with
status 0, but this is wrong.

Add a little regression test.

Reviewed by:	pouria, zlei, melifaro
MFC after:	2 weeks
Sponsored by:	Stormshield
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D54918

0 files changed, 0 insertions, 0 deletions