net: fix network drivers ndo_start_xmit() return values (part 2)

Fix up IRDA drivers that return an errno value to qdisc_restart(), causing
qdisc_restart() to print a warning an requeue/retransmit the skb.

- donauboe: intention appears to be to have the skb retransmitted without
            error message
- irda-usb: intention is to drop silently according to comment
- kingsub-sir: skb is freed: use after free
- ks959-sir: skb is freed: use after free
- ksdazzle-sir: skb is freed: use after free
- mcs7880: skb is freed: use after free

All but donauboe compile tested.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/irda/ksdazzle-sir.c

@@ -304,9 +304,6 @@ static int ksdazzle_hard_xmit(struct sk_buff *skb, struct net_device *netdev)
 	unsigned int wraplen;
 	int ret = 0;
 
-	if (skb == NULL || netdev == NULL)
-		return -EINVAL;
-
 	netif_stop_queue(netdev);
 
 	/* the IRDA wrapping routines don't deal with non linear skb */
@@ -341,7 +338,7 @@ static int ksdazzle_hard_xmit(struct sk_buff *skb, struct net_device *netdev)
 	dev_kfree_skb(skb);
 	spin_unlock(&kingsun->lock);
 
-	return ret;
+	return NETDEV_TX_OK;
 }
 
 /* Receive callback function */