HFP: Let Telephony ignore screen off when listening to signal strength

* Set INDICATION_FILTER_SIGNAL_STRENGTH to INDICATION_UPDATE_MODE_IGNORE_SCREEN_OFF
  when start listening to signal strength update
* Set it back to INDICATION_UPDATE_MODE_NORMAL when we stop listening to
  these updates

Bug: 65112388
Test: make, HeadsetPhoneStateTest,
      connect to carkits, shield device when screen is off

Change-Id: I7d6abe9e1d75b32629daf0a3336c289c3362ea7d