iflib_init_locked() assumes that iflib_stop() has been called, however,
it is not called for media changes.
iflib_if_init_locked() calls stop then init, so fixes the problem.
PR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=253473
MFC after: 3 days
Sponsored by: Juniper Networks, Inc., Klara, Inc.