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>
diff --git a/net/core/dev.c b/net/core/dev.c
index feaab489..d933d1b 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3836,6 +3836,7 @@
 	BUG_ON(!dev_net(dev));
 	net = dev_net(dev);
 
+	spin_lock_init(&dev->addr_list_lock);
 	netdev_init_queue_locks(dev);
 
 	dev->iflink = -1;