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>

arch/um/drivers/net_kern.c

@@ -245,7 +245,7 @@ static int uml_net_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	dev_kfree_skb(skb);
 
-	return 0;
+	return NETDEV_TX_OK;
 }
 
 static void uml_net_set_multicast_list(struct net_device *dev)