batman-adv: fix and simplify condition when bonding should be used

The current condition actually does NOT consider bonding when the
interface the packet came in from is the soft interface, which is the
opposite of what it should do (and the comment describes). Fix that and
slightly simplify the condition.

Reported-by: Ray Gibson <booray@gmail.com>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>

net/batman-adv/routing.c

@@ -443,11 +443,13 @@ batadv_find_router(struct batadv_priv *bat_priv,
 
 	router = batadv_orig_router_get(orig_node, recv_if);
 
+	if (!router)
+		return router;
+
 	/* only consider bonding for recv_if == BATADV_IF_DEFAULT (first hop)
 	 * and if activated.
 	 */
-	if (recv_if == BATADV_IF_DEFAULT || !atomic_read(&bat_priv->bonding) ||
-	    !router)
+	if (!(recv_if == BATADV_IF_DEFAULT && atomic_read(&bat_priv->bonding)))
 		return router;
 
 	/* bonding: loop through the list of possible routers found