On one of the Jenkins agents for macOS Catalina, the `Face/TestMulticastEthernetTransport/NetifStateChange` consistently fails when it attempts to use the `awdl0` (Apple Wireless Direct Link) interface (which is administratively up, but is not RUNNING). DOWN). However, I have confirmed that it still fails on macOS when this test case attempts to use a standard Ethernet interface that is also administratively up, but not RUNNING. DOWN. Davide and I have determined that this issue is likely caused by a combination of the following two issues: * EthernetTransport is not initially set to DOWN when the underlying interface is initially not RUNNING. * EthernetFixture uses any interface that is not DOWN, but the test case in question assumes that the transport is initially RUNNING (not guaranteed).