floss: Trigger LE scan during discovery

Since we treat start/stop discovery as classic only, we need to
start/stop an LE scanner alongside discovery to capture LE devices.
Also set the flag to make discovery classic only.

Bug: 274967984
Tag: #floss
Test: Manual test on ChromeOS with btclient and UI
Change-Id: Ia31171fad6c2644cbe2273d15c705e4e05272a2f