af_ieee802154: drop IEEE802154_SIOC_ADD_SLAVE declaration

IEEE802154_SIOC_ADD_SLAVE was used to allocate 802.15.4 interfaces
on the top of radio. It's not used anymore, drop it.
Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/af_ieee802154.h

@@ -54,7 +54,4 @@ struct sockaddr_ieee802154 {
 	struct ieee802154_addr addr;
 };
 
-/* master device */
-#define IEEE802154_SIOC_ADD_SLAVE		(SIOCDEVPRIVATE + 0)
-
 #endif