mac80211 tells us when we need to dump the frames from the
AGG queue instead of releasing them as single MPDUs.
Being able to differentiate between the different cases
(IEEE80211_AMPDU_TX_STOP_*) allows us to handle races better.

When the station is removed, mac80211 asks to flush and
removes the station right away.
This allows to avoid a case where we still have frames in
AGG queues, but the station has been remove already.

Note that we can have frames on the shared queues, but this
is not a problem: the station in the fw will be kept until
all the frames on the shared queues have been drained.
AGG queues are a special case since they are dynamically
allocated.
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>