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/pcmcia/smc91c92_cs.c

@@ -1388,7 +1388,7 @@ static int smc_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	dev->stats.tx_aborted_errors++;
 	printk(KERN_DEBUG "%s: Internal error -- sent packet while busy.\n",
 	       dev->name);
-	return 1;
+	return NETDEV_TX_BUSY;
     }
     smc->saved_skb = skb;