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/via-velocity.c b/drivers/net/via-velocity.c
index 47be41a..e56cf6b 100644
--- a/drivers/net/via-velocity.c
+++ b/drivers/net/via-velocity.c
@@ -2465,7 +2465,8 @@
  *	Called by the networ layer to request a packet is queued to
  *	the velocity. Returns zero on success.
  */
-static int velocity_xmit(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t velocity_xmit(struct sk_buff *skb,
+				 struct net_device *dev)
 {
 	struct velocity_info *vptr = netdev_priv(dev);
 	int qnum = 0;