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>

drivers/net/acenic.c

@@ -2464,7 +2464,8 @@ ace_load_tx_bd(struct ace_private *ap, struct tx_desc *desc, u64 addr,
 }
 
 
-static int ace_start_xmit(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t ace_start_xmit(struct sk_buff *skb,
+				  struct net_device *dev)
 {
 	struct ace_private *ap = netdev_priv(dev);
 	struct ace_regs __iomem *regs = ap->regs;