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/3c501.c b/drivers/net/3c501.c
index 367bec6..e29fb1a 100644
--- a/drivers/net/3c501.c
+++ b/drivers/net/3c501.c
@@ -485,7 +485,7 @@
 			if (el_debug > 2)
 				pr_debug(" queued xmit.\n");
 			dev_kfree_skb(skb);
-			return 0;
+			return NETDEV_TX_OK;
 		}
 		/* A receive upset our load, despite our best efforts */
 		if (el_debug > 2)