batman-adv: fix neigh reference imbalance

When an interface is removed from batman-adv, the orig_ifinfo of a
orig_node may be removed without releasing the router first.
This will prevent the reference for the neighbor pointed at by the
orig_ifinfo->router to be released, and this leak may result in
reference leaks for the interface used by this neighbor. Fix that.

This is a regression introduced by
7351a482
("batman-adv: split out router from orig_node").
Reported-by: Antonio Quartulli <antonio@open-mesh.com>
Signed-off-by: Simon Wunderlich <simon@open-mesh.com>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>

net/batman-adv/originator.c

@@ -501,12 +501,17 @@ batadv_neigh_node_get(const struct batadv_orig_node *orig_node,
 static void batadv_orig_ifinfo_free_rcu(struct rcu_head *rcu)
 {
 	struct batadv_orig_ifinfo *orig_ifinfo;
+	struct batadv_neigh_node *router;
 
 	orig_ifinfo = container_of(rcu, struct batadv_orig_ifinfo, rcu);
 
 	if (orig_ifinfo->if_outgoing != BATADV_IF_DEFAULT)
 		batadv_hardif_free_ref_now(orig_ifinfo->if_outgoing);
 
+	/* this is the last reference to this object */
+	router = rcu_dereference_protected(orig_ifinfo->router, true);
+	if (router)
+		batadv_neigh_node_free_ref_now(router);
 	kfree(orig_ifinfo);
 }