ToDevice/linuxmodule: Transmit skb with dev_queue_xmit()

If ToDevice sends skbs fast enough so TX desc of netdev is full,
device driver can request stop queuing by calling netif_stop_queue().
In that case dev_watchdog() will think netdev's TX is hung because
txq->trans_start is never updated by ToDevice().
To update txq->trans_start, ToDevice needs to use dev_queue_xmit()

This fixes periodic watchdog timeout:
[  101.895978] ------------[ cut here ]------------
[  101.897175] WARNING: at net/sched/sch_generic.c:266 dev_watchdog+0x1d6/0x288()
[  101.898728] Hardware name: Bochs
[  101.899389] NETDEV WATCHDOG: eth1 (e1000e): transmit queue 0 timed out
[  101.900768] Modules linked in: click proclikefs e1000e
[  101.902532] Pid: 552, comm: kclick Not tainted 2.6.37+ #35
[  101.904416] Call Trace:
[  101.905264]  <IRQ>  [<ffffffff81082946>] warn_slowpath_common+0x80/0x98
[  101.907012]  [<ffffffff810829f2>] warn_slowpath_fmt+0x41/0x43
[  101.908146]  [<ffffffff8143aeee>] dev_watchdog+0x1d6/0x288
[  101.909225]  [<ffffffff810c5a8e>] ? handle_edge_irq+0x187/0x195
[  101.910370]  [<ffffffff814218e5>] ? __napi_complete+0x28/0x31
[  101.911739]  [<ffffffff8108f726>] run_timer_softirq+0x20e/0x300
[  101.913106]  [<ffffffff8143ad18>] ? dev_watchdog+0x0/0x288
[  101.914498]  [<ffffffff81088c26>] __do_softirq+0xe1/0x1b7
[  101.915462]  [<ffffffff8103fb9c>] call_softirq+0x1c/0x30
[  101.916659]  [<ffffffff81041359>] do_softirq+0x61/0xbf
[  101.917657]  [<ffffffff810885ca>] irq_exit+0x36/0x38
[  101.919697]  [<ffffffff8105b13b>] smp_apic_timer_interrupt+0x88/0x96
[  101.920563]  [<ffffffff8103f653>] apic_timer_interrupt+0x13/0x20

Signed-off-by: Joonwoo Park <joonwpark81@gmail.com>

elements/linuxmodule/todevice.cc

@@ -503,8 +503,7 @@ ToDevice::queue_packet(Packet *p, struct netdev_queue *txq)
 #endif
 
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 30)
-    // XXX should we call dev_hard_start_xmit???  Probably
-    ret = dev->netdev_ops->ndo_start_xmit(skb1, dev);
+    ret = dev_queue_xmit(skb1);
 #else
     ret = dev->hard_start_xmit(skb1, dev);
 #endif