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/benet/be_main.c b/drivers/net/benet/be_main.c
index 7b9efee..e19fe1d 100644
--- a/drivers/net/benet/be_main.c
+++ b/drivers/net/benet/be_main.c
@@ -427,7 +427,8 @@
 	return copied;
 }
 
-static int be_xmit(struct sk_buff *skb, struct net_device *netdev)
+static netdev_tx_t be_xmit(struct sk_buff *skb,
+				 struct net_device *netdev)
 {
 	struct be_adapter *adapter = netdev_priv(netdev);
 	struct be_tx_obj *tx_obj = &adapter->tx_obj;