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/net/atm/mpc.c b/net/atm/mpc.c
index e5bf114..1ac4b94 100644
--- a/net/atm/mpc.c
+++ b/net/atm/mpc.c
@@ -554,7 +554,7 @@
 	while (i < mpc->number_of_mps_macs) {
 		if (!compare_ether_addr(eth->h_dest, (mpc->mps_macs + i*ETH_ALEN)))
 			if ( send_via_shortcut(skb, mpc) == 0 )           /* try shortcut */
-				return 0;                                 /* success!     */
+				return NETDEV_TX_OK;                      /* success!     */
 		i++;
 	}