mt76: mt76x02: fix tx status reporting issues

mt76: mt76x02: fix tx status reporting issues

When the hardware falls back to lower rates for a transmit attempt, only the
first status report will show the number of retries correctly. The frames
that follow will report the correct final rate, but number of retries set to 0.
This can cause the rate control module to vastly underestimate the number of
retransmissions per rate.

To fix this, we need to keep track of the initial requested tx rate per packet
and pass it to the status information.
For frames with tx status requested, this is simple: use the rate configured
in info->control.rates[0] as reference.
For no-skb tx status information, we have to encode the requested tx rate in
the packet id (and make it possible to distinguish it from real packet ids).

To do that, reduce the packet id field size by one bit, and use that bit to
indicate packet id vs rate.

This change also improves reporting by filling the status rate array with
rates from first rate to final rate, taking the same steps as the hardware
fallback table. This matters in corner cases like MCS8 on HT, where the
fallback target is MCS0, not MCS7.

Signed-off-by: Felix Fietkau <nbd@nbd.name>