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>

drivers/net/myri10ge/myri10ge.c

@@ -2687,7 +2687,7 @@ again:
 		/* we are out of transmit resources */
 		tx->stop_queue++;
 		netif_tx_stop_queue(netdev_queue);
-		return 1;
+		return NETDEV_TX_BUSY;
 	}
 
 	/* Setup checksum offloading, if needed */