ieee802154: add nl802154 framework

This patch adds a basic nl802154 framework. Most of this code was
grabbed from nl80211 framework.

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

net/ieee802154/netlink.c

@@ -155,7 +155,7 @@ int __init ieee802154_nl_init(void)
 						    ieee802154_mcgrps);
 }
 
-void __exit ieee802154_nl_exit(void)
+void ieee802154_nl_exit(void)
 {
 	genl_unregister_family(&nl802154_family);
 }