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/a2065.c b/drivers/net/a2065.c
index 02f64d5..85a1817 100644
--- a/drivers/net/a2065.c
+++ b/drivers/net/a2065.c
@@ -564,7 +564,7 @@
 
 	if (!TX_BUFFS_AVAIL){
 		local_irq_restore(flags);
-		return -1;
+		return NETDEV_TX_LOCKED;
 	}
 
 #ifdef DEBUG_DRIVER