Add --no-routing argument

[chadbrubaker]

--no-routing will skip the routing setup for tproxy and redirect routing
modes. This is for the case where you want to set up nogotofail traffic
routing in a non-standard mode with your own routing rules. It is up to
the user to properly route traffic to the socket listening on --port.

[chadbrubaker]

This is basically for the case where you want to do custom routing instead of ngtf's assumption that you're a box that's bridging traffic. For example I'm using some UID based rules to do some local testing and want to avoid my scripts needing to blow away the ngtf rules.