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/sonic.c b/drivers/net/sonic.c
index 753a1fb..9599ce7 100644
--- a/drivers/net/sonic.c
+++ b/drivers/net/sonic.c
@@ -211,7 +211,7 @@
 	length = skb->len;
 	if (length < ETH_ZLEN) {
 		if (skb_padto(skb, ETH_ZLEN))
-			return 0;
+			return NETDEV_TX_OK;
 		length = ETH_ZLEN;
 	}
 
@@ -265,7 +265,7 @@
 
 	dev->trans_start = jiffies;
 
-	return 0;
+	return NETDEV_TX_OK;
 }
 
 /*