floss: Scanner: Active scan if no filter, otherwise Passive scan

This is the mitigation for multiple issues + missing features. See
comment for details.

Bug: 328711786
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: 1. Enable Fast Pair, verified scan type is set to Passive
      2. Scanning with Sphero EDU APP, verified Active scan
      3. Stop Sphero EDU APP, verified scan type is back to Passive
Flag: EXEMPT, Floss-only changes
Change-Id: I1cdc6712bf185a0739c043d9a9338a413ecd5e30