mac80211: track only QoS data frames for admission control

[ Upstream commit d5e568c3a4ec2ddd23e7dc5ad5b0c64e4f22981a ]

For admission control, obviously all of that only works for
QoS data frames, otherwise we cannot even access the QoS
field in the header.

Syzbot reported (see below) an uninitialized value here due
to a status of a non-QoS nullfunc packet, which isn't even
long enough to contain the QoS header.

Fix this to only do anything for QoS data packets.

Reported-by:  <syzbot+614e82b88a1a4973e534@syzkaller.appspotmail.com>
Fixes: 02219b3a ("mac80211: add WMM admission control support")
Link: https://lore.kernel.org/r/20211122124737.dad29e65902a.Ieb04587afacb27c14e0de93ec1bfbefb238cc2a0@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>