Add version negotiation to network protocol

[newsch]

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[newsch]

I'm proud to say this is the first time I've thought "this is a good use-case for GOTO"

[MatthewBeaudouinLafon]

I agree it's not a bad use of GOTO, but I'm not convinced it's a good one either?
You could do the exact same thing with a "negotiate protocol" void function, and at a glance the function signature shouldn't even be too bad (especially if you pass rlen as a parameter).
Also if else statements could work, at the cost of some duplicate code (which I assume is why you got stoked about GOTO in the first place).
I vote for the function, but if you do want to keep the GOTO statement, watch your 6.

[newsch]

You could do the exact same thing with a "negotiate protocol" void function, and at a glance the function signature shouldn't even be too bad (especially if you pass rlen as a parameter).

Fair. I'm trying to hold off on refactoring any server code to avoid more merge conflicts with #80, which already restructures a fair bit of it.

I'll rewrite this bit as part of #80.