netdev: Fix lockdep warnings in multiqueue configurations.

When support for multiple TX queues were added, the
netif_tx_lock() routines we converted to iterate over
all TX queues and grab each queue's spinlock.

This causes heartburn for lockdep and it's not a healthy
thing to do with lots of TX queues anyways.

So modify this to use a top-level lock and a "frozen"
state for the individual TX queues.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/dev.c b/net/core/dev.c
index 63d6bcd..69320a5 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4200,6 +4200,7 @@
 {
 	netdev_init_one_queue(dev, &dev->rx_queue, NULL);
 	netdev_for_each_tx_queue(dev, netdev_init_one_queue, NULL);
+	spin_lock_init(&dev->tx_global_lock);
 }
 
 /**