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/bnx2.c b/drivers/net/bnx2.c
index c4e85f6..fcaf3bc 100644
--- a/drivers/net/bnx2.c
+++ b/drivers/net/bnx2.c
@@ -6283,7 +6283,7 @@
  * bnx2_tx_int() runs without netif_tx_lock unless it needs to call
  * netif_wake_queue().
  */
-static int
+static netdev_tx_t
 bnx2_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct bnx2 *bp = netdev_priv(dev);