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>
diff --git a/drivers/net/sky2.c b/drivers/net/sky2.c
index dd630cf..c7c0a5b 100644
--- a/drivers/net/sky2.c
+++ b/drivers/net/sky2.c
@@ -1574,7 +1574,8 @@
  * the number of ring elements will probably be less than the number
  * of list elements used.
  */
-static int sky2_xmit_frame(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t sky2_xmit_frame(struct sk_buff *skb,
+				   struct net_device *dev)
 {
 	struct sky2_port *sky2 = netdev_priv(dev);
 	struct sky2_hw *hw = sky2->hw;