Function response 

pub(crate) fn response(
    req: &Header2,
    status: Status,
    body: Vec<u8>,
    session_id: u64,
) -> Vec<u8> 

Build a 64-byte SMB2 response header + body, echoing MessageId/TreeId and stamping the effective session id ([MS-SMB2] §3.3.4.1).