Bluetooth boot: call doBind only if stack is ready

Calling doBind when the stack is not yet ready is producing very verbose
logging during bluetooth startup.
To avoid that, the registerStateChangeCallback will now always call its
callback when it unregister, and it will also always call it when you
register and the bluetooth is already one.

This is a no-op change from an outsider point of view

Test: Any presubmit run will show profile
Test: atest ServiceBluetoothTests
Bug: 291815510
Change-Id: I9c5ec06da794e1444a38bcb3009456adbe50b34f