333d5e52f5
In S, the behaviour of createTunInterface and createTapInterface changed so that they bring up the interface before returning it. This makes it difficult to test code that brings interfaces up itself, such as IpClient or EthernetManager, because the tests cannot predict whether that code will see the interface up or not. This leads to flaky tests and can even make it impossible to reliably test some behaviour. Add a method that allows the caller to specify whether to bring up the interface or not. Test: new codepath tested by other CL in topic Test: existing codepaths already well-covered Change-Id: I0f7698f4dad132f201db4203e65a78c6af564ab2