Added test coverage regarding how EthernetTracker consumes the xml config as set in config_ethernet_interfaces. Additionally, adding test coverage for transport override functionality in EthernetNetworkFactory. Bug: 206170402 Test: atest com.android.server.ethernet.EthernetTrackerTest && atest com.android.server.ethernet.EthernetNetworkFactoryTest Change-Id: I3d55a230d3f28154ed6fdac6d63ed57bf589d3bd