mac802154: rx: rename remove mac802154_subif_rx

This patch removes the mac802154_subif_rx function and do the necessary
calls inside of ieee802154_rx function. The ieee802154_rx is small
enough to move the functionality inside this function.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>