batman,rcu: convert call_rcu(gw_node_free_rcu) to kfree_rcu

The RCU callback gw_node_free_rcu() just calls kfree(), so we can use
kfree_rcu() instead of call_rcu().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Marek Lindner <lindner_marek@yahoo.de>
Cc: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Acked-by: David S. Miller <davem@davemloft.net>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Acked-by: Sven Eckelmann <sven@narfation.org>

net/batman-adv/gateway_client.c

@@ -28,18 +28,10 @@
 #include <linux/udp.h>
 #include <linux/if_vlan.h>
 
-static void gw_node_free_rcu(struct rcu_head *rcu)
-{
-	struct gw_node *gw_node;
-
-	gw_node = container_of(rcu, struct gw_node, rcu);
-	kfree(gw_node);
-}
-
 static void gw_node_free_ref(struct gw_node *gw_node)
 {
 	if (atomic_dec_and_test(&gw_node->refcount))
-		call_rcu(&gw_node->rcu, gw_node_free_rcu);
+		kfree_rcu(gw_node, rcu);
 }
 
 void *gw_get_selected(struct bat_priv *bat_priv)