Method on_failed

src/brpc/stream.h:51–52

`on_failed` will be called before `on_closed` when the stream is closed abnormally.

    // `on_failed` will be called  before `on_closed`
    // when the stream is closed abnormally.
    virtual void on_failed(StreamId id, int error_code,
                           const std::string& error_text) {}
};

struct StreamOptions {