Replace useTls with mode in PrivateDnsConfig am: 707915c012

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

Change-Id: Iff3ef9c72612e3f576f160b79ca99ea71cac9f83
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>