Downloading in chunks with PullAll and Offset+MaxCount was originally brought
up for issue #72112. The purpose mentioned there (being able to stop the sync
between chunks) was better addressed with the Bluez 5.15 suspend/resume API.

However, downloading in chunks is useful for another purpose: just downloading
large address books (5000 contacts, 8KB photo data in each contact) from slow
devices (Samsung Galaxy S3) can take 45 minutes.

If the driver always turns off the car after a 15 minute commute, he'll never
get the entire address book cached. Downloading in chunks can help by starting
the download at varying offsets.

The downside is that the PBAP spec doesn't support downloading in chunks
reliably if contacts get deleted during the download.