net: kill dev->master

Nobody uses this now. Remove it.
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1169,10 +1169,6 @@ struct net_device {
 						 * avoid dirtying this cache line.
 						 */
 
-	struct net_device	*master; /* Pointer to master device of a group,
-					  * which this device is member of.
-					  */
-
 	struct list_head	upper_dev_list; /* List of upper devices */
 
 	/* Interface address info used in eth_type_trans() */