batman-adv: call unregister_netdev() to have it handle the locking for us

Reported-by: NSven Eckelmann <sven@narfation.org>
Signed-off-by: NMarek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: NAntonio Quartulli <antonio@meshcoding.com>

net/batman-adv/soft-interface.c

@@ -652,10 +652,7 @@ static void batadv_softif_destroy_finish(struct work_struct *work)
 	}
 
 	batadv_sysfs_del_meshif(soft_iface);
-
-	rtnl_lock();
-	unregister_netdevice(soft_iface);
-	rtnl_unlock();
+	unregister_netdev(soft_iface);
 }
 
 /**