[nearby] Add discoveryTimestamp field am: a34d7e8949 am: 4c0aa8bf15

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2871218

Change-Id: I06a69fb7271c416d997ae1aad32eb08f11b79583
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>