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/wan/dlci.c b/drivers/net/wan/dlci.c
index e8d155c..2fa275a 100644
--- a/drivers/net/wan/dlci.c
+++ b/drivers/net/wan/dlci.c
@@ -205,15 +205,15 @@
 	{
 		case DLCI_RET_OK:
 			dev->stats.tx_packets++;
-			ret = 0;
+			ret = NETDEV_TX_OK;
 			break;
 			case DLCI_RET_ERR:
 			dev->stats.tx_errors++;
-			ret = 0;
+			ret = NETDEV_TX_OK;
 			break;
 			case DLCI_RET_DROP:
 			dev->stats.tx_dropped++;
-			ret = 1;
+			ret = NETDEV_TX_BUSY;
 			break;
 	}
 	/* Alan Cox recommends always returning 0, and always freeing the packet */