Replace useTls with mode in PrivateDnsConfig am: 707915c012 am: f5f4c0071d

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

Change-Id: I7b7e399fe2e04605583ffca78b78374552e55cc0
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>