ath11k: report tx bitrate for iw wlan station dump

HTT_T2H_MSG_TYPE_PPDU_STATS_IND is a message which include the ppdu
info, currently it is not report from firmware for ath11k, then the
tx bitrate of "iw wlan0 station dump" always show an invalid value
"tx bitrate: 6.0 MBit/s".

To address the issue, this is to parse the info of tx complete report
from firmware and indicate the tx rate to mac80211.

After that, "iw wlan0 station dump" show the correct tx bit rate such
as:
tx bitrate: 78.0 MBit/s MCS 12
tx bitrate: 144.4 MBit/s VHT-MCS 7 short GI VHT-NSS 2
tx bitrate: 286.7 MBit/s HE-MCS 11 HE-NSS 2 HE-GI 0 HE-DCM 0
tx bitrate: 1921.5 MBit/s 160MHz HE-MCS 9 HE-NSS 2 HE-GI 0 HE-DCM 0

Tested-on: QCA6390 hw2.0 PCI WLAN.HST.1.0.1-01740-QCAHSTSWPLZ_V2_TO_X86-1

Signed-off-by: Wen Gong <quic_wgong@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20211217093722.5739-1-quic_wgong@quicinc.com