mac802154: iface: assume big endian for af_packet

The callback "create" and "parse" from header_ops are called from
netdev core upper-layer functionality, like af_packet. These callbacks
assumes big endian for addresses and we should not introduce a special
byteordering handling for ieee802154 over af_packet in userspace.

We have an identical issue with setting the mac address which also
assumes big endian byteordering.

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