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/7990.c b/drivers/net/7990.c
index 69f5b7d..b1e5764 100644
--- a/drivers/net/7990.c
+++ b/drivers/net/7990.c
@@ -585,7 +585,7 @@
 		lp->tx_full = 1;
 	spin_unlock_irqrestore (&lp->devlock, flags);
 
-        return 0;
+        return NETDEV_TX_OK;
 }
 EXPORT_SYMBOL_GPL(lance_start_xmit);