Merge "[Thread] leverage the TestableNetworkAgent to simplify the setup of test network" into main am: ad3ca8bbb4

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/3545746

Change-Id: Ib0b3750bf353e9ad9b205034c77b477a659d9630
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>