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/ethoc.c b/drivers/net/ethoc.c
index 4dbe5f1..b871aef 100644
--- a/drivers/net/ethoc.c
+++ b/drivers/net/ethoc.c
@@ -802,7 +802,7 @@
 	return &priv->stats;
 }
 
-static int ethoc_start_xmit(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t ethoc_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct ethoc *priv = netdev_priv(dev);
 	struct ethoc_bd bd;