TODO(jeffyjf) Now, we just provide a spice discriminator, so we return it directly.

The discriminator confirmed the protocol of the tunnel's traffic and extra all properties of the protocol.

The discriminator confirmed the protocol of the tunnel's traffic isn't the protocol of the discriminator.

The max lenght of the traffic header data which the quic-tun will cache them and use them to classify traffic.

The procotol already confirmed, but need more data to fill properties.

The index of the server link message's message size.

The discriminator can't confirm the protocol of the tunnel's traffic, means need more data.