Clearing streams from port in interlaced mode.

[apepelis]

if you put the port in Interlaced mode and then try to delete all streams (issue 179), there is a 53 second pause.

    _sid_list = drone.getStreamIdList(port_string.port_id[0])
    drone.deleteStream(sid_list)

    # https://github.com/pstavirs/ostinato/issues/179
    stream_cfg = ost_pb.StreamConfigList()
    stream_cfg.port_id.id = port_string.port_id[0].id
    drone.modifyStream(stream_cfg)_

this needs to be added

    _port_id_list = drone.getPortIdList()
    port_config_list = drone.getPortConfig(port_id_list)
    for port in port_config_list.port:
        if port.port_id == port_string.port_id[0]:
            port.transmit_mode = ost_pb.kSequentialTransmit
            break
    drone.modifyPort(port_config_list)_

to change it to sequential