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/8139too.c b/drivers/net/8139too.c
index b39ec98..4a36287 100644
--- a/drivers/net/8139too.c
+++ b/drivers/net/8139too.c
@@ -628,8 +628,8 @@
 static void rtl8139_start_thread(struct rtl8139_private *tp);
 static void rtl8139_tx_timeout (struct net_device *dev);
 static void rtl8139_init_ring (struct net_device *dev);
-static int rtl8139_start_xmit (struct sk_buff *skb,
-			       struct net_device *dev);
+static netdev_tx_t rtl8139_start_xmit (struct sk_buff *skb,
+				       struct net_device *dev);
 #ifdef CONFIG_NET_POLL_CONTROLLER
 static void rtl8139_poll_controller(struct net_device *dev);
 #endif
@@ -1687,7 +1687,8 @@
 	}
 }
 
-static int rtl8139_start_xmit (struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t rtl8139_start_xmit (struct sk_buff *skb,
+					     struct net_device *dev)
 {
 	struct rtl8139_private *tp = netdev_priv(dev);
 	void __iomem *ioaddr = tp->mmio_addr;