Merge "Add a method to help mocking registerNetworkAgent" into main am: 13a5d4b36e

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/3543704

Change-Id: I234ac8bf938052ba1a1c5fc1d9734657b7b08481
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>