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/s390/net/netiucv.c b/drivers/s390/net/netiucv.c
index 8c36eaf..bb1183a 100644
--- a/drivers/s390/net/netiucv.c
+++ b/drivers/s390/net/netiucv.c
@@ -1376,14 +1376,14 @@
 	if (skb == NULL) {
 		IUCV_DBF_TEXT(data, 2, "netiucv_tx: skb is NULL\n");
 		privptr->stats.tx_dropped++;
-		return 0;
+		return NETDEV_TX_OK;
 	}
 	if (skb_headroom(skb) < NETIUCV_HDRLEN) {
 		IUCV_DBF_TEXT(data, 2,
 			"netiucv_tx: skb_headroom < NETIUCV_HDRLEN\n");
 		dev_kfree_skb(skb);
 		privptr->stats.tx_dropped++;
-		return 0;
+		return NETDEV_TX_OK;
 	}
 
 	/**
@@ -1395,7 +1395,7 @@
 		privptr->stats.tx_dropped++;
 		privptr->stats.tx_errors++;
 		privptr->stats.tx_carrier_errors++;
-		return 0;
+		return NETDEV_TX_OK;
 	}
 
 	if (netiucv_test_and_set_busy(dev)) {