ieee802154: 6lowpan: earlier skb->dev switch

We should change the skb->dev pointer earlier to the lowpan interface
Sometimes we call iphc_decompress which also use some netdev printout
functionality. This patch will change that the correct interface will be
displayed in this case, which should be the lowpan interface.

Reviewed-by: Stefan Schmidt <stefan@osg.samsung.com>
Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>