batman-adv: Use kref_get for batadv_tvlv_container_get

batadv_tvlv_container_get requires that tvlv.container_list_lock is held by
the caller. It is therefore not possible that an item in
tvlv.container_list has an reference counter of 0 and is still in the list

The kref_get function instead WARNs (with debug information) when the
reference counter would still be 0. This makes a bug in batman-adv better
visible because kref_get_unless_zero would have ignored this problem.
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a@unstable.cc>

net/batman-adv/main.c

@@ -748,9 +748,7 @@ batadv_tvlv_container_get(struct batadv_priv *bat_priv, u8 type, u8 version)
 		if (tvlv_tmp->tvlv_hdr.version != version)
 			continue;
 
-		if (!kref_get_unless_zero(&tvlv_tmp->refcount))
-			continue;
-
+		kref_get(&tvlv_tmp->refcount);
 		tvlv = tvlv_tmp;
 		break;
 	}