FR: optionally add new interface as default routing

[mgaulton]

Hi There,
Your app fills a need mostly that I have.
I run my VPN in a namespace and run applications in it, to allow my host namespace to be used for other things.
I have a few dockerized apps that can't be installed on my host, so I'm trying to figure out how to link the docker to the VPN namespace to get to the internet.
I'd like to be able to designate which is the client and which is the tunnel, and have the ability to tell the client to change its default route to the tunnel link.
Any help or suggestions would be great

Thank you for your work!