net: use symbolic values for ndo_start_xmit() return codes

Convert magic values 1 and -1 to NETDEV_TX_BUSY and NETDEV_TX_LOCKED respectively.

0 (NETDEV_TX_OK) is not changed to keep the noise down, except in very few cases
where its in direct proximity to one of the other values.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/cassini.c b/drivers/net/cassini.c
index f522276..eb06667 100644
--- a/drivers/net/cassini.c
+++ b/drivers/net/cassini.c
@@ -2934,7 +2934,7 @@
 	 *      individual queues.
 	 */
 	if (cas_xmit_tx_ringN(cp, ring++ & N_TX_RINGS_MASK, skb))
-		return 1;
+		return NETDEV_TX_BUSY;
 	dev->trans_start = jiffies;
 	return 0;
 }