Add ECM exit listener.

- Add ECM exist listener which listens for the
ACTION_EMERGENCY_CALLBACK_MODE_CHANGED intent; use this to trigger
notification to the current connections so that they can update themselves
to indicate they support Mute if ECM mode is disabled.
- Fixes a bug where ECM exits after a non-emerg connection starts; the
connection does not update itself to allow mute now that ECM is disabled.
- Also, fixed minor bug in CallTracker which would cause a crash when
trying to test emergency calls on IMS which does not have a
CommandInterface (mCI) instance.

Bug: 23044098
Change-Id: I3aef7b2f7e73d3496aac21a0e910316eee6ec22a