net_maxfilesize is a console variable available in all games.
net_maxfilesize Allow servers to download large map files, sounds, textures and models to your computer without hassle.
"The server is running my map fine but clients get 'missing BSP' message??"
You will need to edit your server.cfg file for this. Your server.cfg file should be in your cfg folder. The limit for net_maxfilesize is 64. Setting net_maxfilesize to this value will allow clients to download content which is 64MB or smaller in size.
net_maxfilesize only affects slow downloads via the Source Dedicated Server.