qcacld-3.0: Add ini to honour NL80211 scan policy flags

Currently dwell time is determined by scan policy flags from kernel.
Sometimes when we suspect the scan result is not full enough, we need
to set dwell time by force through ini.

Add ini to decide whether to honour NL80211 scan policy flags, so that
we can disable dwell time changed by scan policy flag from kernel.

Change-Id: Ia0b9f957a7de901513479522e008e4bcbd6b2c0e
CRs-Fixed: 2428630