batman-adv: avoid NULL dereferences and fix if check

Gateway having bandwidth_down equal to zero are not accepted
at all and so never added to the Gateway list.
For this reason checking the bandwidth_down member in
batadv_gw_out_of_range() is useless.

This is probably a copy/paste error and this check was supposed
to be "!gw_node" only. Moreover, the way the check is written
now may also lead to a NULL dereference.

Fix this by rewriting the if-condition properly.

Introduced by 414254e3
("batman-adv: tvlv - gateway download/upload bandwidth container")
Signed-off-by: NAntonio Quartulli <antonio@meshcoding.com>
Reported-by: NDavid Binderman <dcb314@hotmail.com>
Signed-off-by: NMarek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/batman-adv/gateway_client.c

@@ -810,7 +810,7 @@ bool batadv_gw_out_of_range(struct batadv_priv *bat_priv,
 		goto out;
 
 	gw_node = batadv_gw_node_get(bat_priv, orig_dst_node);
-	if (!gw_node->bandwidth_down == 0)
+	if (!gw_node)
 		goto out;
 
 	switch (atomic_read(&bat_priv->gw_mode)) {