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/macb.c b/drivers/net/macb.c
index 7222659..5b5c253 100644
--- a/drivers/net/macb.c
+++ b/drivers/net/macb.c
@@ -645,7 +645,7 @@
 			"BUG! Tx Ring full when queue awake!\n");
 		dev_dbg(&bp->pdev->dev, "tx_head = %u, tx_tail = %u\n",
 			bp->tx_head, bp->tx_tail);
-		return 1;
+		return NETDEV_TX_BUSY;
 	}
 
 	entry = bp->tx_head;