Function ask_reply 

pub fn ask_reply() -> Chunk

Atomic request/reply via Opcode::Ask (RPC hop).

Requires crate::std_native_table.

1. main builds Message { id=1, tag=REQ, payload=41 } and Asks the server Cap
2. server ReceiveMatchImm TAG_REQ, replies via msg_reply_cap with TAG_REP / payload 42 and the same request_id
3. Ask resumes with the reply; main returns payload 42