net: add NL802154 interface for configuration of 802.15.4 devices

Add a netlink interface for configuration of IEEE 802.15.4 device. Also this
interface specifies events notification sent by devices towards higher layers.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Sergey Lapin <slapin@ossfans.org>
Signed-off-by: David S. Miller <davem@davemloft.net>