Replace useTls with mode in PrivateDnsConfig am: 707915c012 am: 313a10fb75

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

Change-Id: I7e6f8f2b5b9e8d06ee06cfe55373987f70aad8a1
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>