vnc: factor out vnc_update_server_surface Signed-off-by: Gerd Hoffmann <kraxel@redhat.com> Reviewed-by: Peter Lieven <pl@kamp.de> Reviewed-by: Daniel P. Berrange <berrange@redhat.com> Message-id: 1446203414-4013-13-git-send-email-kraxel@redhat.com