Add support for forwarded ports

[wuservices]

It'd be great if Forwarded Ports worked with vagrant-linode like it does with the built-in providers.

It seems like this isn't currently implemented, as I have something like this but nothing gets forwarded:
config.vm.network 'forwarded_port', guest: 3000, host: 3060

As a workaround, I can use the following, but having it built in, makes it easier to have a consistent setup for everybody sharing the same Vagrantfile without having to add extra arguments.
vagrant ssh -- -L 3060:localhost:3000

However, if this should work and I'm just doing it wrong, please let me know :)