Send back an error if we get unexpected stream control message

Send back an error if we get unexpected stream control message

We ignore any stream data packets which come in for streams which
are not registered, since these packets are async and do not have
a reply. If we get a stream control packet though we must send back
an actual error, otherwise a (broken) client may hang forever
making it hard to diagnose the client bug.

* src/rpc/virnetserverprogram.c: Send back error for unexpected
  stream control messages