doc: http.IncomingMessage.statusMessage description out of place

[`statusMessage`](https://nodejs.org/api/http.html#http_message_statusmessage) description lost its place and is under `socket`.

See f4c259ab942a371c7b71408ce2a38c1f90d7211d / https://github.com/nodejs/node/pull/3662.
