ath10k: add the Rx rate in FW stats

FW stats does provide the Rx rate information. Add this.
Tested with firmware 10x firmware.

Increase buffer size so more peers can be shown.

Signed-off-by: Chun-Yeow Yeoh <yeohchunyeow@gmail.com>
Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>