net: Implement for_each_netdev_reverse.

I will need this shortly to implement network namespace shutdown
batching.  For sanity sake network devices should be removed in
the reverse order they were created in.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1112,6 +1112,8 @@ extern rwlock_t				dev_base_lock;		/* Device list lock */
 
 #define for_each_netdev(net, d)		\
 		list_for_each_entry(d, &(net)->dev_base_head, dev_list)
+#define for_each_netdev_reverse(net, d)	\
+		list_for_each_entry_reverse(d, &(net)->dev_base_head, dev_list)
 #define for_each_netdev_rcu(net, d)		\
 		list_for_each_entry_rcu(d, &(net)->dev_base_head, dev_list)
 #define for_each_netdev_safe(net, d, n)	\