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/e100.c b/drivers/net/e100.c
index 119dc53..e52a201 100644
--- a/drivers/net/e100.c
+++ b/drivers/net/e100.c
@@ -1716,7 +1716,7 @@
 		/* This is a hard error - log it. */
 		DPRINTK(TX_ERR, DEBUG, "Out of Tx resources, returning skb\n");
 		netif_stop_queue(netdev);
-		return 1;
+		return NETDEV_TX_BUSY;
 	}
 
 	netdev->trans_start = jiffies;