HTTP Server Stops Responding to Any/All Requests

### Version 14.18.1 ### Platform IBM i 7.4 ### Subsystem http ### What steps will reproduce the bug? The HTTP server can suddenly stop responding to any and all requests. When the server gets into this state it will remain listening and accepting client connections but will stop running the `requestListener` callback, so clients will suddenly stop getting responses to any request. When the server gets into this state, there is no output at stdout/stderr and the behavior persists for the duration of the process. The problem is intermittent and it's not clear what causes it, but it seems to be triggered by certain network activity. The only way I can reproduce it on demand is by running a network vulnerability scan against the server using Nessus Essentials, and having the server running in multiple processes using `cluster`. To be clear, I have seen the problem occur many times during normal use of the HTTP server without any network scans taking place. I have also seen it happen without `cluster` in play. This is just the only way I have found to reliably reproduce it. To reproduce, run this simple server on IBM i: ``` if (cluster.isMaster) { cluster.fork(); } else { const server = http.createServer((req, res) => { console.log(new Date(), "request received"); res.writeHead( 200, { "Content-Type": "text/plain", "Cache-Control": "no-store" } ); res.end("OK"); }); server.on("listening", () => { console.log("Listening on port", PORT); }); server.listen(PORT); } ``` Then run a Basic Network Scan using Nessus Essentials: https://www.tenable.com/downloads/nessus I've been using Nessus 8.15.2 and running it on Windows 10. To setup the scan: 1. Click "New Scan" 2. Choose the Basic Network Scan  3. Enter your Node HTTP server IP under Targets ![image](https://user-images.githubusercontent.com/3142160/…