Replace useTls with mode in PrivateDnsConfig am: 707915c012

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

Change-Id: I9e09a63c1945a0eeb77487b6e9f1ab3f7662b784
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>