PBAP: Reload contacts on user switch

When the active user changes, update contacts.

The car kit will still have the old contacts, but when it
asks for new contacts it will get contacts for the new user.

Bug: 72435402
Test: Connect and disconnect to a car kit, switch users, repeat
Change-Id: Ia015aa5b3d6dece4515d76bb1804e2c1ba05e349