qcacld-3.0: fix improper data rate in rtap header in monitor mode

In ht monitor mode, mcs data rate is not correctly populated in
radiotap header, so if ht_flag is set, assign mcs value to ht_mcs
to fix it.

Change-Id: If428275671068b31ae1367244c62bc4cac25a2af
CRs-Fixed: 2772405