batman-adv: prevent potential hlist double deletion

The hlist_del_rcu() call in batadv_tt_global_size_mod() does not check
if the element still is part of the list prior to deletion. The atomic
list counter should prevent the worst but converting to
hlist_del_init_rcu() ensures the element can't be deleted more than
once.
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>

net/batman-adv/translation-table.c

@@ -315,7 +315,7 @@ static void batadv_tt_global_size_mod(struct batadv_orig_node *orig_node,
 
 	if (atomic_add_return(v, &vlan->tt.num_entries) == 0) {
 		spin_lock_bh(&orig_node->vlan_list_lock);
-		hlist_del_rcu(&vlan->list);
+		hlist_del_init_rcu(&vlan->list);
 		spin_unlock_bh(&orig_node->vlan_list_lock);
 		batadv_orig_node_vlan_free_ref(vlan);
 	}