r8169: RTNL and flush_scheduled_work deadlock

flush_scheduled_work() in net_device->close has a slight tendency
to deadlock with tasks on the workqueue that hold RTNL.

rtl8169_close/down simply need the recovery tasks to not meddle
with the hardware while the device is going down.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>