Initialize the SDL_net library.
Returns 0 on success, -1 on error; call SDL_GetError() for details.
This must be successfully called once before (almost) any other SDL_net function can be used.
It is safe to call this multiple times; the library will only initialize once, and won't deinitialize until SDLNet_Quit() has been called a matching number of times. Extra attempts to init report success.
It is safe to call this function from any thread.
This function is available since SDL_net 3.0.0.