Add logging to TestableNetworkCallback. am: 3f6b8dfd10 am: 3d1fbd23a0

Original change: https://android-review.googlesource.com/c/platform/frameworks/libs/net/+/1526366

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I6572bd329b84cf58f3213a93ad9b2f414a55b6a1