floss: btmanagerd: Treat TurningOff as enabled states

In TurningOff state the Start call is actually not actionable. Treating
it as enabled means we send out OnHciEnabledChanged after the internal
state has changed from TurningOff to Off. Thus clients could safely call
Start whenever they received the callback.

Bug: 301164021
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: Toggle BT quickly through UI, the swich won't auto disable

Change-Id: I2d9036ca4b9b23dc547027b2995b9afcf4be675f