net: convert remaining non-symbolic return values in ndo_start_xmit() functions

This patch converts the remaining occurences of raw return values to their
symbolic counterparts in ndo_start_xmit() functions that were missed by the
previous automatic conversion.

Additionally code that assumed the symbolic value of NETDEV_TX_OK to be zero
is changed to explicitly use NETDEV_TX_OK.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/skfp/skfddi.c b/drivers/net/skfp/skfddi.c
index 0c31272..888a14a 100644
--- a/drivers/net/skfp/skfddi.c
+++ b/drivers/net/skfp/skfddi.c
@@ -1077,7 +1077,7 @@
 		// dequeue packets from xmt queue and send them
 		netif_start_queue(dev);
 		dev_kfree_skb(skb);
-		return (0);	/* return "success" */
+		return NETDEV_TX_OK;	/* return "success" */
 	}
 	if (bp->QueueSkb == 0) {	// return with tbusy set: queue full