net: refactor sslconfig to not depend on LuaSec This now requires that the network backend exposes a tls_builder function, which essentially wraps the former util.sslconfig.new() function, passing a factory to create the eventual SSL context. That allows a net.server backend to pick whatever it likes as SSL context factory, as long as it understands the config table passed by the SSL config builder. Heck, a backend could even mock and replace the entire SSL config builder API.