Merge "Store registered network callbacks and unregister all at tearDown" am: 0eca785322

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2479276

Change-Id: I10a23866aed769be2edfe4db2a05b698e7ae87b2
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>