Use iflib_if_init_locked() during media change instead of iflib_init_locked().

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: 253473
MFC after: 3 days
Reviewed by: markj
Sponsored by: Juniper Networks, Inc., Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D28667