zebra: On shutdown stop hook calls for fpm rmac updates

When shutting down zebra, the hook for the rmac update was
not being unregistered.  As such it would be possible
to get into a condition where more rmacs are being
added to the queue for handling in the future after we
are told to shutdown.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>

zebra/zebra_fpm.c

@@ -2049,6 +2049,8 @@ static int zfpm_fini(void)
 	zfpm_stop_stats_timer();
 
 	hook_unregister(rib_update, zfpm_trigger_update);
+	hook_unregister(zebra_rmac_update, zfpm_trigger_rmac_update);
+
 	return 0;
 }