netdev: Add addr_list_lock to struct net_device.

This will be used to protect the per-device unicast and multicast
address lists, as well as the callbacks into the drivers which
configure such state such as ->set_rx_mode() and ->set_multicast_list().

Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -609,6 +609,7 @@ struct net_device
 	unsigned char		addr_len;	/* hardware address length	*/
 	unsigned short          dev_id;		/* for shared network cards */
 
+	spinlock_t		addr_list_lock;
 	struct dev_addr_list	*uc_list;	/* Secondary unicast mac addresses */
 	int			uc_count;	/* Number of installed ucasts	*/
 	int			uc_promisc;