CTS test for eth manager allowed UIDs

CTS tests for using the EthernetManager#updateConfiguration API to
set NetworkCapabilities.Builder#setAllowedUids functionality.

Bug: 210487893
Test: atest CtsNetTestCases
:android.net.cts.EthernetManagerTest --iterations

Change-Id: Iefb2e49bd6c05c9cf9ae678bd94b39b051664584