Added debug system property to enable/disable IMS VoLTE/VT.

If property is 0: IMS VoLTE is disabled.
If property is 1 then IMS is used as normal: i.e. expected to
be provisioned, registered etc.

Action on missing property defined by constant.

Change-Id: Ibdbb21fa7db30a4088b74092dd6256da012cd697
1 file changed