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/natsemi.c b/drivers/net/natsemi.c
index 32db12a2..bd41351 100644
--- a/drivers/net/natsemi.c
+++ b/drivers/net/natsemi.c
@@ -621,7 +621,7 @@
 static void free_ring(struct net_device *dev);
 static void reinit_ring(struct net_device *dev);
 static void init_registers(struct net_device *dev);
-static int start_tx(struct sk_buff *skb, struct net_device *dev);
+static netdev_tx_t start_tx(struct sk_buff *skb, struct net_device *dev);
 static irqreturn_t intr_handler(int irq, void *dev_instance);
 static void netdev_error(struct net_device *dev, int intr_status);
 static int natsemi_poll(struct napi_struct *napi, int budget);
@@ -2079,7 +2079,7 @@
 	reinit_rx(dev);
 }
 
-static int start_tx(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t start_tx(struct sk_buff *skb, struct net_device *dev)
 {
 	struct netdev_private *np = netdev_priv(dev);
 	void __iomem * ioaddr = ns_ioaddr(dev);