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/mac89x0.c b/drivers/net/mac89x0.c
index e24175a..dab4533 100644
--- a/drivers/net/mac89x0.c
+++ b/drivers/net/mac89x0.c
@@ -400,7 +400,7 @@
 		/* Gasp!  It hasn't.  But that shouldn't happen since
 		   we're waiting for TxOk, so return 1 and requeue this packet. */
 		local_irq_restore(flags);
-		return 1;
+		return NETDEV_TX_BUSY;
 	}
 
 	/* Write the contents of the packet */