mac802154: rename mac802154_sub_if_data

Like wireless this structure should named ieee802154_sub_if_data and not
mac802154_sub_if_data. This patch renames the struct and variables to
sdata instead priv sometimes.

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