iwlwifi: mvm: support using multiple ACs on single HW queue

"DQA" is shorthand for "dynamic queue allocation", with the
idea of allocating queues per-RA/TID on-demand rather than
using shared queues statically allocated per vif. The goal
of this is to enable future features (like GO PM) and to
improve performance measurements of TX traffic.

When RA/TID streams can't be neatly sorted into different AC
queues, DQA allows sharing queues for the same RA. This means
that DQA allows different ACs may reach the same HW queue.

Update the code to allow such queue sharing by having a mapping
between the HW queue and the mac80211 queues using it (as this
could be more than one queue).

Signed-off-by: Liad Kaufman <liad.kaufman@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>