Whitelist BLE advertising

Currently when advertising the library accepts connections from any device. It would be nice to be able to use the whitelist feature to restrict the incoming connections to previously bonded peers only. That way it would be possible to replicate the behavior of most consumer Bluetooth devices, where they normally only connect with known peers and you have to specifically request pairing mode by pressing a dedicated button.

Start by locating the BLE advertising and whitelist support in the library, then trace how bonded peers are represented and checked during incoming connections. Confirm the expected behavior for advertising with whitelist mode enabled: previously bonded peers can connect, while unknown devices cannot unless pairing mode is explicitly requested.

Written by the indexing model from the issue text.