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/sh_eth.c b/drivers/net/sh_eth.c
index 0709b75..341882f 100644
--- a/drivers/net/sh_eth.c
+++ b/drivers/net/sh_eth.c
@@ -1108,7 +1108,7 @@
 		if (!sh_eth_txfree(ndev)) {
 			netif_stop_queue(ndev);
 			spin_unlock_irqrestore(&mdp->lock, flags);
-			return 1;
+			return NETDEV_TX_BUSY;
 		}
 	}
 	spin_unlock_irqrestore(&mdp->lock, flags);