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/sfc/selftest.c b/drivers/net/sfc/selftest.c
index b67ccca..817c7ef 100644
--- a/drivers/net/sfc/selftest.c
+++ b/drivers/net/sfc/selftest.c
@@ -400,7 +400,8 @@
 	struct efx_loopback_state *state = efx->loopback_selftest;
 	struct efx_loopback_payload *payload;
 	struct sk_buff *skb;
-	int i, rc;
+	int i;
+	netdev_tx_t rc;
 
 	/* Transmit N copies of buffer */
 	for (i = 0; i < state->packet_count; i++) {