Support VSNCP

[rdcloyi]

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This is very good PPP implementation in Golang. I'd like to use it to support VSNCP on the base of LCP since all negotiation procedures are in common. But currently the Pkt structure is only for IPCP/LCP. Would it be better to use an Interface instead of concrete Pkt structure so that I can have own Serialize/Parse implementation for VSNCP?

[hujun-open]

what is the use case? VSNCP is not commonly used protocol;