Replace useTls with mode in PrivateDnsConfig am: 707915c012

Original change: https://android-review.googlesource.com/c/platform/packages/modules/NetworkStack/+/2841436

Change-Id: I620b3bd11b90190ffbb6968dd517dd2b9a41d12b
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>