Add PRIVATE_DNS_MODE setting setter am: 6865eb6dda

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1654014

Change-Id: I97de83147a0c656802601ec116ee9ee7de114884
tree: e6b968b3c405d3d1cfbcc28e81cc7990825d0353
  1. framework/
  2. service/
  3. OWNERS
  4. TEST_MAPPING