+		default: /* Drivers are not supposed to return other values! */
+			if (net_ratelimit())
+				pr_info("pktgen: %s xmit error: %d\n",
+					odev->name, ret);
 			pkt_dev->errors++;

I believe this is faulty.  Things like vlans can send pkts to qdiscs
of the underlying device and those can return other values.

Patric McHardy put in some patches recently to achieve this in a more
uniform manner:

http://patchwork.ozlabs.org/patch/28340/

Thanks,
Ben

-- 
Ben Greear [off-list ref] 
Candela Technologies Inc  http://www.candelatech.com