'callback of telnet option. It gets called when option is activated.
This one here is used to detect when the client agrees on RFC 2217. A
flag is set so that other functions like check_modem_lines know if the
client is OK.'

def _client_ok(self):

    self._client_is_rfc2217 = True
    if self.logger:
        self.logger.info('client    accepts    RFC    2217')
    self.check_modem_lines(force_notification=True)
