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/dnet.c b/drivers/net/dnet.c
index 2818d5d..2346852 100644
--- a/drivers/net/dnet.c
+++ b/drivers/net/dnet.c
@@ -541,7 +541,7 @@
 #define dnet_print_skb(skb)	do {} while (0)
 #endif
 
-static int dnet_start_xmit(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t dnet_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 
 	struct dnet *bp = netdev_priv(dev);