This moves all parts in the Duke/Redneck modules that access ENet into net.cpp/network.cpp and changes global ENet structs to use C++ notation instead of typedefs so that anonymous definitions for them can be added where needed.
These changes are done to avoid including enet.h globally which is a major issue because this file does not work without including windows.h, making it extremely dirty.
When doing this during startup it can be done by regular cleanup measures.
This also moves two larger chunks of networking code out of game.cpp.
Nevertheless, the fact that enet is a very dirty library which directly depends on Windows types is a big problem because it bleeds Windows definitions everywhere thanks to poor abstraction in all relevant layers.
