Allow for remote to be a private ip

[mmlb]

IsPublicIP is called from Parse, this applies even if we've configured AllowedSubnets. I'd still argue IsPublicIP does not belong as a filter by default since there's no reason why a proxy must be globally addressable (think entirely private services), but that could be a dangerous change to make at this point.

I'd be happy to come up with a PR for this, is there some form you'd like to see this implemented?

[SpoonOne]

We have a staging environment which is on private addressing and this affects us as well. We would like to be able to have the remote IP be a private IP.