Floss: Cancel discovery before BREDR pairing/connection

If BREDR connection is to be executed, e.g. in create_bond and
connect_all_enabled_profiles, we should cancel discovery first because
some of the connection-related HCI commands may be rejected by the
Bluetooth controller when Inquiry is in progress.

With background scanning migration to LE Scan API, the Discovery API is
redefined to not guarantee continuous discovery forever, but instead
clients are notified via callbacks when discovery is stopped by the
stack. Because of this simplification of the API, we don't need to
resume discovery after connection or pairing is complete.

Bug: 211127013
Tag: #floss
Test: Manual - Perform pairing with BREDR device via UI

Change-Id: I6f4d8ecbbeb1b7a7a9dc3193431edba2b4e05e51