Added silenced verification before notifying headset.

When at least one headset is not silenced,
HeadsetPhoneState will notify HeadsetService which will
notify all HeadsetStateMachines. This adds a check to
ensure the device is not silenced before notifying it
of the state changes.

Tag: #stability
Bug: 204097820
Test: manual
Change-Id: Icb6b9c98bf85030e8e3bff7480628733ba0c715e