mac802154: fix byteorder issues

Running make C=2 occurs these warnings:

cast from restricted __be64
incorrect type in argument 1 (different base types)
expected unsigned long long[unsigned] [usertype] val
got restricted __be64 [usertype]<noident>
cast from restricted __be64
cast to restricted __le64

This patch fix these warnings by forcing to __le64 type and using swabp64
instead swab64.

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