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/ibmveth.c b/drivers/net/ibmveth.c
index 76b295a..5862282 100644
--- a/drivers/net/ibmveth.c
+++ b/drivers/net/ibmveth.c
@@ -887,7 +887,8 @@
 
 #define page_offset(v) ((unsigned long)(v) & ((1 << 12) - 1))
 
-static int ibmveth_start_xmit(struct sk_buff *skb, struct net_device *netdev)
+static netdev_tx_t ibmveth_start_xmit(struct sk_buff *skb,
+				      struct net_device *netdev)
 {
 	struct ibmveth_adapter *adapter = netdev_priv(netdev);
 	union ibmveth_buf_desc desc;