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/ppp_generic.c b/drivers/net/ppp_generic.c
index 639d11b..d0b9655 100644
--- a/drivers/net/ppp_generic.c
+++ b/drivers/net/ppp_generic.c
@@ -988,12 +988,12 @@
 	netif_stop_queue(dev);
 	skb_queue_tail(&ppp->file.xq, skb);
 	ppp_xmit_process(ppp);
-	return 0;
+	return NETDEV_TX_OK;
 
  outf:
 	kfree_skb(skb);
 	++dev->stats.tx_dropped;
-	return 0;
+	return NETDEV_TX_OK;
 }
 
 static int