em(4): Always reinit interface when adding/removing VLAN

This partially reverts r361053 since there have been reports
by users that this breaks some functionality for em(4)
devices; it seems at first glance that some sort of interface
restart is required for those cards.

This isn't a proper fix; this unbreaks those users until a proper
fix is found for their issues.

PR:		240818
Reported by:	Marek Zarychta <zarychtam@plan-b.pwste.edu.pl>
MFC after:	3 days

sys/dev/e1000/if_em.c

@@ -4059,7 +4059,6 @@ em_if_needs_restart(if_ctx_t ctx __unused, enum iflib_restart_event event)
 {
 	switch (event) {
 	case IFLIB_RESTART_VLAN_CONFIG:
-		return (false);
 	default:
 		return (true);
 	}