Bluetooth: 6lowpan: change netdev_priv to lowpan_dev

The usually way to get the btle lowpan private data is to use the
introduced lowpan_dev inline function. This patch will cleanup by using
lowpan_dev consequently.
Reviewed-by: NStefan Schmidt <stefan@osg.samsung.com>
Signed-off-by: NAlexander Aring <alex.aring@gmail.com>
Signed-off-by: NMarcel Holtmann <marcel@holtmann.org>

net/bluetooth/6lowpan.c

@@ -859,7 +859,7 @@ static int setup_netdev(struct l2cap_chan *chan, struct lowpan_dev **dev)
 	SET_NETDEV_DEV(netdev, &chan->conn->hcon->hdev->dev);
 	SET_NETDEV_DEVTYPE(netdev, &bt_type);
 
-	*dev = netdev_priv(netdev);
+	*dev = lowpan_dev(netdev);
 	(*dev)->netdev = netdev;
 	(*dev)->hdev = chan->conn->hcon->hdev;
 	INIT_LIST_HEAD(&(*dev)->peers);