Function build_response 

pub fn build_response(
    optional_support: u16,
    service: &str,
    native_fs: &str,
    unicode: bool,
    params_base_abs: usize,
) -> (Vec<u8>, Vec<u8>)

Build the WC=4 response (AndX triple + OptionalSupport) with the service and native-filesystem strings in the buffer.