Fix interaction between BluetoothEventLoop and BluetoothService.

BluetoothEventLoop primarily handles event notifications from Bluez.
It should know innards of Bonding and especially BondState.
BondState class and BluetoothService call into each other.
When BluetoothEvent loop gets the handle to BondState it leads
to deadlocks and ANRs.

Change-Id: I785c57f6246c1288350d26d4acb87d879b27a5f9