iwlwifi: enable communication with WoWLAN firmware

On resuming, the opmode may have to be able to talk
to the WoWLAN/D3 firmware in order to query it about
its status and wakeup reasons. To do that, the opmode
has to call the new d3_resume() transport API which
will set up the device for command communcation.

Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>