ath10k: add per peer tx stats support for 10.2.4

10.2.4 firmware branch (used in QCA988X) does not support
HTT_10_4_T2H_MSG_TYPE_PEER_STATS and that's why ath10k does not provide
tranmission rate statistics to user space, instead it just shows
hardcoded 6 Mbit/s. But pktlog firmware facility provides per peer tx
statistics. The firmware sends one pktlog event for every four
PPDUs per peer, which include:

* successful number of packets and bytes transmitted
* number of packets and bytes dropped
* retried number of packets and bytes
* rate info per ppdu

Firmware supports WMI_SERVICE_PEER_STATS, pktlog is enabled through
ATH10K_FLAG_PEER_STATS, which is nowadays enabled by default in ath10k.

This patch does not impact throughput.

Tested on QCA9880 with firmware version 10.2.4.70.48. This should also
work with firmware branch 10.2.4-1.0-00029

Parse peer stats from pktlog packets and update the tx rate information
per STA. This way user space can query about transmit rate with iw:

$iw wlan0 station dump
Station 3c:a9:f4:72:bb:a4 (on wlan1)
        inactive time:  8210 ms
        rx bytes:       9166
        rx packets:     44
        tx bytes:       1105
        tx packets:     9
        tx retries:     0
        tx failed:      1
        rx drop misc:   3
        signal:         -75 [-75, -87, -88] dBm
        signal avg:     -75 [-75, -85, -88] dBm
        tx bitrate:     39.0 MBit/s MCS 10
        rx bitrate:     26.0 MBit/s MCS 3
        rx duration:    23250 us
        authorized:     yes
        authenticated:  yes
        associated:     yes
        preamble:       short
        WMM/WME:        yes
        MFP:            no
        TDLS peer:      no
        DTIM period:    2
        beacon interval:100
        short preamble: yes
        short slot time:yes
        connected time: 22 seconds

Signed-off-by: Anilkumar Kolli <akolli@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>