Forbid ForwardOpen/ForwardClose from Host application

System test has discovered that we just crash when they send a FwOpen over the DPM Mailbox. Decision is to forbid ForwardOpen and ForwardClose over the DPM (CIP_SERVICE_REQ) and reject the requests with appropriate status code.

We may consider this again in the future, as one can think of use cases where this might make sense, like tunneling of CIP through other networks or any other Direct Forwarding between two different CIP networks. For now, we will not implement class 1 connections initiated through the DPM.