[Thread] add CTS test for registerNetworkCallback for Thread

To make sure that apps can register for Thread network by specifying
only TRANSPORT_THREAD.

This prevents regression given aosp/2873154 was considered a short-term
solution.

Bug: 313000440
Test: atest CtsThreadNetworkTestCases:android.net.thread.cts.ThreadNetworkControllerTest#threadNetworkCallback_deviceAttached_threadNetworkIsAvailable
Change-Id: I7860c50b092439f39e5d8c437de1863b0633b7a0