Add dtmSupported into 1.6 HAL for 2G network am: fb3fa529b2 am: c1f27e9269

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/1574925

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Iaa709d812aa3d3d814533ad18037685ce2574e88