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/8390p.c b/drivers/net/8390p.c
index d225c29..a2a64ea 100644
--- a/drivers/net/8390p.c
+++ b/drivers/net/8390p.c
@@ -22,7 +22,7 @@
 }
 EXPORT_SYMBOL(eip_close);
 
-int eip_start_xmit(struct sk_buff *skb, struct net_device *dev)
+netdev_tx_t eip_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	return __ei_start_xmit(skb, dev);
 }