qcacld-3.0: dual-band option is missing under AP Band in Hotspot

To show the "dual-band" option in "AP Band" in Hotspot, the host
should set the feature flag of CONCURRENT_BAND_SESSIONS in
hardware's capability and sends it to userspace.

The fix is to set the CONCURRENT_BAND_SESSIONS feature flag and
send it to userspace via the QCA_NL80211_VENDOR_SUBCMD_GET_FEATURES
vendor command.

Change-Id: If29c35be4ea86c966624922f0209b1e5c272d405
CRs-Fixed: 2968554