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>
diff --git a/drivers/net/irda/irda-usb.c b/drivers/net/irda/irda-usb.c
index 394b2b1..0c0831c 100644
--- a/drivers/net/irda/irda-usb.c
+++ b/drivers/net/irda/irda-usb.c
@@ -389,7 +389,6 @@
 	s32 speed;
 	s16 xbofs;
 	int res, mtt;
-	int	err = 1;	/* Failed */
 
 	IRDA_DEBUG(4, "%s() on %s\n", __func__, netdev->name);
 
@@ -430,7 +429,6 @@
 			irda_usb_change_speed_xbofs(self);
 			netdev->trans_start = jiffies;
 			/* Will netif_wake_queue() in callback */
-			err = 0;	/* No error */
 			goto drop;
 		}
 	}
@@ -542,7 +540,7 @@
 	/* Drop silently the skb and exit */
 	dev_kfree_skb(skb);
 	spin_unlock_irqrestore(&self->lock, flags);
-	return err;		/* Usually 1 */
+	return NETDEV_TX_OK;
 }
 
 /*------------------------------------------------------------------*/