net: Allow for more then a single subclass for netif_addr_lock

Currently netif_addr_lock_nested assumes that there can be only
a single nesting level between 2 devices.  However, if we
have multiple devices of the same type stacked, this fails.
For example:
 eth0 <-- vlan0.10 <-- vlan0.10.20

A more complicated configuration may stack more then one type of
device in different order.
Ex:
  eth0 <-- vlan0.10 <-- macvlan0 <-- vlan1.10.20 <-- macvlan1

This patch adds an ndo_* function that allows each stackable
device to report its nesting level.  If the device doesn't
provide this function default subclass of 1 is used.
Signed-off-by: NVlad Yasevich <vyasevic@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1144,6 +1144,7 @@ struct net_device_ops {
 	netdev_tx_t		(*ndo_dfwd_start_xmit) (struct sk_buff *skb,
 							struct net_device *dev,
 							void *priv);
+	int			(*ndo_get_lock_subclass)(struct net_device *dev);
 };
 
 /**
@@ -2950,7 +2951,12 @@ static inline void netif_addr_lock(struct net_device *dev)
 
 static inline void netif_addr_lock_nested(struct net_device *dev)
 {
-	spin_lock_nested(&dev->addr_list_lock, SINGLE_DEPTH_NESTING);
+	int subclass = SINGLE_DEPTH_NESTING;
+
+	if (dev->netdev_ops->ndo_get_lock_subclass)
+		subclass = dev->netdev_ops->ndo_get_lock_subclass(dev);
+
+	spin_lock_nested(&dev->addr_list_lock, subclass);
 }
 
 static inline void netif_addr_lock_bh(struct net_device *dev)