websocket: reduce memory usage

[tsctx]

> $ node memory.js // before
memoryUsage: 104Kib
> $ node memory.js // after
memoryUsage: 68Kib

const socket = new WebSocket("ws://localhost:5001")

socket.onopen = function () {
    const rss = process.memoryUsage.rss()
    socket.send("hi")
    socket.onmessage = function () {
        console.log(`memoryUsage: ${(process.memoryUsage.rss() - rss) / 1024}Kib`)
        socket.close()
    }
}

Refs: websockets/ws@ddfe4a8

[tsctx]

It is effective because it can greatly reduce memory at the same performance.

[mcollina]

lgtm