For legacy mode, tx bitrate not show correct sometimes, for example:
iw wlan0 link
Connected to 8c:21:0a:b3:5a:64 (on wlan0)
        SSID: tplinkgw
        freq: 2462
        RX: 19672 bytes (184 packets)
        TX: 9851 bytes (87 packets)
        signal: -51 dBm
        rx bitrate: 54.0 MBit/s
        tx bitrate: 2.8 MBit/s

This patch use the tx bitrate info from WMI_TLV_PEER_STATS_INFO_EVENTID
report from firmware, and tx bitrate show correct.

iw wlan0 link
Connected to 8c:21:0a:b3:5a:64 (on wlan0)
        SSID: tplinkgw
        freq: 2462
        RX: 13973 bytes (120 packets)
        TX: 6737 bytes (57 packets)
        signal: -52 dBm
        rx bitrate: 54.0 MBit/s
        tx bitrate: 54.0 MBit/s

This patch only effect SDIO chip, ath10k_mac_sta_get_peer_stats_info
has check for bitrate_statistics of hw_params, it is enabled only for
"qca6174 hw3.2 sdio".

Tested with QCA6174 SDIO with firmware WLAN.RMH.4.4.1-00042.
Signed-off-by: Wen Gong <wgong@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200427080416.8265-5-wgong@codeaurora.org