Checks is enhanced route refresh capability is enabled/valid.

        Checks sent and received `Open` messages to see if this session with
        peer is capable of enhanced route refresh capability.

def is_enhanced_rr_cap_valid(self):
        """Checks is enhanced route refresh capability is enabled/valid.

        Checks sent and received `Open` messages to see if this session with
        peer is capable of enhanced route refresh capability.
        """
        if not self.recv_open_msg:
            raise ValueError('Did not yet receive peers open message.')

        err_cap_enabled = False
        local_caps = self.sent_open_msg.opt_param
        peer_caps = self.recv_open_msg.opt_param

        local_cap = [cap for cap in local_caps
                     if cap.cap_code == BGP_CAP_ENHANCED_ROUTE_REFRESH]
        peer_cap = [cap for cap in peer_caps
                    if cap.cap_code == BGP_CAP_ENHANCED_ROUTE_REFRESH]

        # Both local and peer should advertise ERR capability for it to be
        # enabled.
        if local_cap and peer_cap:
            err_cap_enabled = True

        return err_cap_enabled