Remove references to port 655 from MeshLink.

Remove references to port 655 from MeshLink.

First of all, port 655 is officially registered as the port for tinc,
not for any other application. Second, applications built on top of
MeshLink will probably run as non-root, and so cannot bind to ports
lower than 1024 anyway.

- Never try binding to port 655 when setting up a new node.
- Always require a valid port number when making connections.