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>

net/sched/sch_teql.c

@@ -338,7 +338,7 @@ restart:
 
 	if (busy) {
 		netif_stop_queue(dev);
-		return 1;
+		return NETDEV_TX_BUSY;
 	}
 	dev->stats.tx_errors++;