mac802154: remove pib lock

This patch removes the pib lock which is now replaced by rtnl lock. The
new interface already use the rtnl lock only. Nevertheless this patch
will fix issues while using new and old interface at the same time.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Reviewed-by: Stefan Schmidt <stefan@osg.samsung.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>