Improves service state changed notification

The service of GsmCdmaPhone and ImsPhone are changed independently, but
the service state tracker only notify the service state of
GsmCdmaPhone. This changed make the ServiceStateTracker notify the
merged state of GsmCdmaPhone and ImsPhone even if these two phone change
their service state independently.

Bug: 67471135
Test: manually test and unit test

Change-Id: Iba99fc2b02ae536897d9cde07d81b6ab64b5a9cb