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/slip.c b/drivers/net/slip.c
index 5c61d5f..899c4a2 100644
--- a/drivers/net/slip.c
+++ b/drivers/net/slip.c
@@ -484,12 +484,12 @@
 		spin_unlock(&sl->lock);
 		printk(KERN_WARNING "%s: xmit call when iface is down\n", dev->name);
 		dev_kfree_skb(skb);
-		return 0;
+		return NETDEV_TX_OK;
 	}
 	if (sl->tty == NULL) {
 		spin_unlock(&sl->lock);
 		dev_kfree_skb(skb);
-		return 0;
+		return NETDEV_TX_OK;
 	}
 
 	sl_lock(sl);
@@ -498,7 +498,7 @@
 	spin_unlock(&sl->lock);
 
 	dev_kfree_skb(skb);
-	return 0;
+	return NETDEV_TX_OK;
 }