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/arcnet/arcnet.c b/drivers/net/arcnet/arcnet.c
index 7d227cda..75a5725 100644
--- a/drivers/net/arcnet/arcnet.c
+++ b/drivers/net/arcnet/arcnet.c
@@ -591,7 +591,8 @@
 
 
 /* Called by the kernel in order to transmit a packet. */
-int arcnet_send_packet(struct sk_buff *skb, struct net_device *dev)
+netdev_tx_t arcnet_send_packet(struct sk_buff *skb,
+				     struct net_device *dev)
 {
 	struct arcnet_local *lp = netdev_priv(dev);
 	struct archdr *pkt;