SFF doesnt handle ARP messages from TcpProxy SFs

Service Functions (SFs) of type TcpProxy send ARP messages to the Service Function Forwarder (SFF) to be able to find where the client and servers are so the SF can establish TCP connections with them.

I think the solution is for the SFF to act as an ARP proxy by replying to the SF with an ARP response so that the SF will then send all traffic to the SFF.

This needs to be solved on stable/lithium and on beryllium master.