batman-adv: select an internet gateway if none was chosen

This is a regression introduced by: 2265c141086474bbae55a5bb3afa1ebb78ccaa7c
("batman-adv: gateway election code refactoring")

Reported-by: Nicolás Echániz <nicoechaniz@codigosur.org>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Acked-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/batman-adv/gateway_client.c

@@ -200,11 +200,11 @@ void batadv_gw_election(struct batadv_priv *bat_priv)
 	if (atomic_read(&bat_priv->gw_mode) != BATADV_GW_MODE_CLIENT)
 		goto out;
 
-	if (!batadv_atomic_dec_not_zero(&bat_priv->gw_reselect))
-		goto out;
-
 	curr_gw = batadv_gw_get_selected_gw_node(bat_priv);
 
+	if (!batadv_atomic_dec_not_zero(&bat_priv->gw_reselect) && curr_gw)
+		goto out;
+
 	next_gw = batadv_gw_get_best_gw_node(bat_priv);
 
 	if (curr_gw == next_gw)