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/mcs7780.c

@@ -824,10 +824,6 @@ static int mcs_hard_xmit(struct sk_buff *skb, struct net_device *ndev)
 	int wraplen;
 	int ret = 0;
 
-
-	if (skb == NULL || ndev == NULL)
-		return -EINVAL;
-
 	netif_stop_queue(ndev);
 	mcs = netdev_priv(ndev);
 
@@ -870,7 +866,7 @@ static int mcs_hard_xmit(struct sk_buff *skb, struct net_device *ndev)
 
 	dev_kfree_skb(skb);
 	spin_unlock_irqrestore(&mcs->lock, flags);
-	return ret;
+	return NETDEV_TX_OK;
 }
 
 static const struct net_device_ops mcs_netdev_ops = {