netdev: convert bulk of drivers to netdev_tx_t

In a couple of cases collapse some extra code like:
   int retval = NETDEV_TX_OK;
   ...
   return retval;
into
   return NETDEV_TX_OK;

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/au1000_eth.c

@@ -937,7 +937,7 @@ static int au1000_close(struct net_device *dev)
 /*
  * Au1000 transmit routine.
  */
-static int au1000_tx(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t au1000_tx(struct sk_buff *skb, struct net_device *dev)
 {
 	struct au1000_private *aup = netdev_priv(dev);
 	struct net_device_stats *ps = &dev->stats;