Add service change handle for Hearing Aids

When receive service changed indication from Hearing Aid (which indicates
Hearing Aid service changed), it will refresh the hearing aid attribute
handle to ensure the attribute handle is correct.

Bug: 122008481
Test: 1.run unit test
2.After Pair old version FW HearingAid, Disconnect/Reconnect new version
FW HearingAId, then check whether HearingAid is working fine.
3.After Pair old version FW HearingAid, Bluetooth off/on to reconnect
new version FW HearingAId, then check whether HearingAid is working
fine.
Change-Id: I48eae10a3016429f35f4f904752be93bb419d515