qcacld-3.0: Rectify the max rates being sent

Currently in the driver, the max rates that are being sent to the
userspace do not take into account the value of the ini
enable_vht20_mcs9. This ini state that the connection doesn't support
MCS9 rates for vht20. As this is not taken into account, the rates
being sent are incorrect.

Add a check inside hdd_report_max_rate to check the value of the ini
before filling up the max MCS index.

Change-Id: I39742b7cc6a18c3d7693a6efef05987ec0e80cec
CRs-Fixed: 2453759