Function build_ioctl_resp 

pub fn build_ioctl_resp(
    file_id: FileId,
    ctl_code: u32,
    output: &[u8],
) -> Vec<u8> 

Build an IOCTL response body (§2.2.32.1). Fixed part is 48 bytes; StructureSize mirrors smbd (49); output lands 8-byte aligned after it.