From what I can tell, the code that the patch covered is responsible for configuring the network interface as a client.

If another system on the phone brings up the interface as a host device to tether internet to a second device, you end up with the phone trying to configure the interface both as a router and as a client.

This. In general interface names are arbitrary and not a good way to determine anything about what it's connected to, but the usb vs eth distinction is particularly bad, because linux will use either for either 'end' of a link.

Unfortunately, test interfaces have to match `testtap\d+`