iwlwifi: mvm: fix PS-Poll enablement

We added the uAPSD enabled ACs and that made the
firmware choose to pull frames with uAPSD trigger
frames instead of PS-Poll.
Fix that.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>