iwlwifi: dvm: fix WoWLAN

My commit below introduced a mutex in the transport to
prevent concurrent operations. To do so, it added a flag
(is_down) to make sure the transport is in the right state.
This uncoverred an bug that didn't cause any harm until
now: iwldvm calls stop_device and then starts the firmware
without calling start_hw in between. While this flow is
fine from the device configuration point of view (register,
etc...), it is now forbidden by the new is_down flag.
This led to this error to appear:
iwlwifi 0000:05:00.0: Can't start_fw since the HW hasn't been started
and the suspend would fail.

This fixes:
https://bugzilla.kernel.org/show_bug.cgi?id=109591



CC: <stable@vger.kernel.org> [4.3+]
Reported-by: Bogdan Bogush <bogdan.s.bogush@gmail.com>
Fixes=fa9f3281 ("iwlwifi: pcie: lock start_hw / start_fw / stop_device")
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>