wifi: ath11k: Send HT fixed rate in WMI peer fixed param

Due to the firmware behavior with HT fixed rate setting,
HT fixed rate MCS with NSS > 1 are treated as NSS = 1
HT rates in the firmware and enables the HT fixed rate of
NSS = 1.

This leads to HT fixed rate is always configured for NSS = 1
even though the user sets NSS = 2 or > 1 HT fixed MCS in the
set bitrate command.

Currently HT fixed MCS is sent via WMI peer assoc command.
Fix this issue, by sending the HT fixed rate MCS in WMI peer
fixed param instead of sending in peer assoc command.

Tested-on: QCN9074 hw1.0 PCI WLAN.HK.2.7.0.1-01744-QCAHKSWPL_SILICONZ-1

Signed-off-by: Maharaja Kennadyrajan <quic_mkenna@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230504092033.3542456-3-quic_mkenna@quicinc.com