It removes the need for undoing the padding changes to skb->data and it
improves performance by eliminating one tx status lookup per MPDU in the
status path. It is also useful for preparing a follow-up fix to better
handle powersave filtering.

A side effect is that these counters, available via debugfs, become now invalid:

* dot11TransmittedFragmentCount
* dot11FrameDuplicateCount,
* dot11ReceivedFragmentCount
* dot11MulticastReceivedFrameCount
Signed-off-by: Felix Fietkau <nbd@nbd.name>
[kvalo@qca.qualcomm.com: add a note about counters, thanks to Zefir Kurtisi]
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>