HFP: Only reset AG indicator listeners when HF is first connected

* Only reset AG indicator listener state in HeadsetStateMachine
  when entering Connected state from Connecting state

Bug: 80408316
Test: Connect a headset that does not need RSSI, make a phone call,
      hangup and check AG indicator listener states
Change-Id: I6422102fab1e12c412890aae84ac471237817ff4
(cherry picked from commit 384c62b8)