ath10k: add extra check for frame tracing

Frames are logged via tracing in two slices:
header and payload, separately. This is done for
performance reasons when one wants to, e.g.
analyse metadata only of frames only.

If for some reason device delivered a frame buffer
which was sized below what 802.11 header implied
tracing logic would blow doing an invalid memory
accesses.

I've hit this problem when running IBSS on QCA988X
with 999.999.0.636 and tracing at the same time.

Fixes: 5ce8e7fd

 ("ath10k: handle ieee80211 header and payload tracing separately")
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>