Bluetooth: Fix test for lookup_dev return value

The condition wouldn't have previously caused -ENOENT to be returned if
dev was NULL. The proper condition should be if (!dev || !dev->netdev).
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/6lowpan.c

@@ -330,7 +330,7 @@ int bt_6lowpan_recv(struct l2cap_conn *conn, struct sk_buff *skb)
 		return -ENOENT;
 
 	dev = lookup_dev(conn);
-	if (dev && !dev->netdev)
+	if (!dev || !dev->netdev)
 		return -ENOENT;
 
 	err = recv_pkt(skb, dev->netdev, conn);