Replace useTls with mode in PrivateDnsConfig am: 707915c012 am: 017a0bf0ba am: f78c08cdb3

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

Change-Id: I2898b68ede21cf6c38a1d12dca8620213d959cb9
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>