Improve type safety for packet buffer

[ghananigans]

The Packet buffer currently holds only fields that are only set by some layer and then read by layers above it. Lower layers "promise" to never touch upper layers' fields.

E.g. Network layer adds network layer information and transport layer uses that when processing a packet. The link layer never touches those fields.

We should consider improving the type safety of the packet buffer by wrapping lower layer types with a new type that has its layer's information.

E.g. Instead of

struct Packet {
    NetworkLayerInfo
    LinkLayerInfo

    pkt
}

We can use

struct LinkPacket {
    LinkLayerInfo

    pkt
}

struct NetworkPacket {
    NetworkLayerInfo
    LinkLayerInfo

    pkt
}

An alternative is to wrap lower layer types with another layer's type (LinkPacket in a NetworkPacket) or some other idea.

cc @tamird @hbhasker

[github-actions[bot]]

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[ayushr2]

@manninglucas is this still relevant?

[manninglucas]

I think it's more appropriate to have the enhancement label here. It's not really an issue right now, but could be a good idea to implement in the future. This idea also probably needs more detailed design work.