batman-adv: Use kref_get for batadv_gw_node_add

batadv_gw_node_add requires that the caller already has a valid reference
for orig_node. It is therefore not possible that it has an reference
counter of 0 and was still given to this function

The kref_get function instead WARNs (with debug information) when the
reference counter would still be 0. This makes a bug in batman-adv better
visible because kref_get_unless_zero would have ignored this problem.
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a@unstable.cc>

net/batman-adv/gateway_client.c

@@ -440,15 +440,11 @@ static void batadv_gw_node_add(struct batadv_priv *bat_priv,
 	if (gateway->bandwidth_down == 0)
 		return;
 
-	if (!kref_get_unless_zero(&orig_node->refcount))
-		return;
-
 	gw_node = kzalloc(sizeof(*gw_node), GFP_ATOMIC);
-	if (!gw_node) {
-		batadv_orig_node_put(orig_node);
+	if (!gw_node)
 		return;
-	}
 
+	kref_get(&orig_node->refcount);
 	INIT_HLIST_NODE(&gw_node->list);
 	gw_node->orig_node = orig_node;
 	gw_node->bandwidth_down = ntohl(gateway->bandwidth_down);