iwlwifi: mvm: handle FRAME_RELEASE in MQ code

For some reason, the FRAME_RELEASE message handling for the
default queue ended up being in the only/default queue for
non-RSS devices; fix that and handle FRAME_RELEASE properly
on the default queue for RSS devices.

Fixes: 585a6fcc ("iwlwifi: mvm: infrastructure for frame-release message")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>