iwlwifi: mvm: use iwl_mvm_mac_get_queues_mask() more

There are a few places that can call the function
iwl_mvm_mac_get_queues_mask() instead of open-coding the
equivalent, so do that. This requires changing it to return
the multicast queue as part of the bitmap, which broke GO
mode because including it in the broadcast station queues
seems to confuse the firmware, so work around that.

Also, the API defines that the CAB queue shouldn't be
included in the TFD queue mask, adjust the comment
accordingly (not a bug).

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