wcn36xx: Track SNR and RSSI for each RX frame

The BDs for each RX frame contain both the RSSI and SNR for the received
frame. If we track and store this information it can be useful to us in
get_survey() and potentially elsewhere.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220115001646.3981501-4-bryan.odonoghue@linaro.org