Add developer setting and system API for inband ringing support

* Add 1 system API to check inband ringing flag in config.xml
	static isInbandRingingSupported(Context)
* Add developer menu options to enable this feature

Bug: 19171297
Test: mm -j 40, HFP regression testing, testplans/82144
Change-Id: Iaf56ea41911f546bbc7ae1f82e399d0f8d48f75f