netdev: convert pseudo drivers to netdev_tx_t

These are all drivers that don't touch real hardware.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/slip.c b/drivers/net/slip.c
index 899c4a2..26f6ee9 100644
--- a/drivers/net/slip.c
+++ b/drivers/net/slip.c
@@ -474,7 +474,7 @@
 
 
 /* Encapsulate an IP datagram and kick it into a TTY queue. */
-static int
+static netdev_tx_t
 sl_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct slip *sl = netdev_priv(dev);