Sequentially handle enable and disable

* Replace thread sleeps in MESSAGE_ENABLE and MESSAGE_DISABLE to delay
  messages. To make sure we do not block the state change process while
  waiting for a state change callback.
* Prevent handling enable or disable at the same time by deferring the
  the request when we are enabling or disabling Bluetooth.

Bug: 128569058
Test: Manual
Change-Id: I2301ba22b6c10fcea71e3b66eea3ea0a0d7f0475
Merged-In: I2301ba22b6c10fcea71e3b66eea3ea0a0d7f0475