net: use NETDEV_TX_OK instead of 0 in ndo_start_xmit() functions

This patch is the result of an automatic spatch transformation to convert
all ndo_start_xmit() return values of 0 to NETDEV_TX_OK.

Some occurences are missed by the automatic conversion, those will be
handled in a seperate patch.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 8d88dae..3700c49 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -558,12 +558,12 @@
 
 	spin_unlock_irq(&np->tx_lock);
 
-	return 0;
+	return NETDEV_TX_OK;
 
  drop:
 	dev->stats.tx_dropped++;
 	dev_kfree_skb(skb);
-	return 0;
+	return NETDEV_TX_OK;
 }
 
 static int xennet_close(struct net_device *dev)