#9 raise max datagram size for network games (optional?)

[Eric Wasylishen]

Currently the max datagram size (i.e. unreliable messages) is 1400 for networked games and 32000 for local.
https://sourceforge.net/p/quakespasm/code/HEAD/tree/trunk/quakespasm/Quake/sv_main.c#l954

The idea is by staying under 1400 bytes the UDP packets won't be fragmented so there's less chance of dropped / delayed packets.
However, this means some heavier maps/mods (e.g. ad_swampy.bsp in arcane dimensions) that QS supports in singleplayer are pretty much unplayable in multiplayer even on a LAN.. you get "packet overflow" messages and entities disappear.

I'm thinking we could copy DirectQ and use a higher max datagram size (our normal max of 32000) if the protocol is 666/999, and use 1024 bytes if the protocol is 15?
https://github.com/AAS/directq/blob/ced5ada2ce0c3f47fa532b01832b1eb4bec81a3b/DirectQ/sv_main.cpp#L1578

Needs to be changed with care (testing compat with other protocol 666 engines like Fitz0.85, MarkV).