UPSTREAM: mac80211: Add txq flags to debugfs

Might help one figure out why aqm drivers may fail to transmit
frames sometimes.

Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

BUG=b:131197056
TEST=Wifi stress and latency under load test
(cherry picked from commit 25b0ba7e)

Signed-off-by: Kan Yan <kyan@google.com>

Change-Id: Iea8d38dc8ed8dee862f66f7768e9b363552460ab
Reviewed-on: https://chromium-review.googlesource.com/1636896


Tested-by: Kan Yan <kyan@google.com>
Commit-Ready: Kan Yan <kyan@google.com>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Julan Hsu <julanhsu@google.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Kan Yan <kyan@chromium.org>