Floss: pause discovery during bond and connect

This patch introduces a mechanism that temporarily prevents clients
from restarting discovery, rather than just canceling it. The patch
prevents clients and Floss from repeatedly starting and stopping
discovery.

Bug: 277977567
Tag: #floss
Test: Manual - Pairing don't triggers the start/stop discovery loop
Change-Id: Iea707981ca1a38d463d461bb1696e98a5b29ecba