mt76: mt7615: sync with mt7603 rate control changes

- Store the previous and current rate set in the driver + the TSF value
  at the time of the switch.
- Use the tx status TSF value to determine which rate set needs to be used
  as reference.
- Report only short or long GI rates for a single status event, not a mix.
- The hardware reports the last used rate index. Use it along with the
  retry count to figure out what rate was used for the first attempt.
- Use the same retry count value for all rate slots to make this calculation
  work.
- Derive the probe rate from the current rateset instead of the skb cb
- Do not wait for a status report for the probe frame before removing the
  probe rate from the rate table. Do it immediately after it was referenced
  in a tx status report.
- Use the first half of the first rate retry budget for the probe rate
  in order to avoid using too many retries on that rate
- Switch from lower rates to higher rates more conservatively
- enable hardware rate up/down selection

Reviewed-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>