Ignore SPEAKER_OFF in ActiveSpeakerRoute after BT become active.

Currently, ActiveSpeakerRoute will handle SPEAKER_OFF by re-evaluate
baseline route of the device. In the case that the SPEAKER_OFF triggered
by a BT connection request, we may mistakenly switch the BT connection to
another unexpected device. Fix this by ignore the SPEAKER_OFF message in
this case.

Bug: 283198536
Test: CallAudioRouteStateMachineTest
Change-Id: I9823173281431c1ff0f39984e1d3237e58bbf23d
Merged-In: I9823173281431c1ff0f39984e1d3237e58bbf23d