mac802154: remove wpan_dev parameter in if_add

This parameter was grabbed from wireless implementation with the
identically wireless dev struct. We don't need this right now and so we
remove it. Maybe we will add it later again if we found any real reason
to have such parameter.

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