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/82596.c b/drivers/net/82596.c
index 996cc91..ea6b139 100644
--- a/drivers/net/82596.c
+++ b/drivers/net/82596.c
@@ -356,7 +356,7 @@
 	0x7f /*  *multi IA */ };
 
 static int i596_open(struct net_device *dev);
-static int i596_start_xmit(struct sk_buff *skb, struct net_device *dev);
+static netdev_tx_t i596_start_xmit(struct sk_buff *skb, struct net_device *dev);
 static irqreturn_t i596_interrupt(int irq, void *dev_id);
 static int i596_close(struct net_device *dev);
 static void i596_add_cmd(struct net_device *dev, struct i596_cmd *cmd);
@@ -1054,8 +1054,7 @@
 	netif_wake_queue (dev);
 }
 
-
-static int i596_start_xmit(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t i596_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct i596_private *lp = dev->ml_priv;
 	struct tx_cmd *tx_cmd;