quic: clarifying code comments

PR-URL: #34283
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/internal/quic/core.js

@@ -717,6 +717,13 @@ class QuicEndpoint {
 
     this[kHandle] = undefined;
     handle[owner_symbol] = undefined;
+    // Calling waitForPendingCallbacks starts the process of
+    // closing down the QuicEndpoint. Once all pending writes
+    // to the underlying libuv udp handle have completed, the
+    // ondone callback will be invoked, triggering the UDP
+    // socket to be closed. Once it is closed, we notify
+    // the QuicSocket that this QuicEndpoint has been closed,
+    // allowing it to be freed.
     handle.ondone = () => {
       state.udpSocket.close((err) => {
         if (err) error = err;
@@ -747,6 +754,7 @@ class QuicEndpoint {
     return {};
   }
 
+  // On Windows, this always returns undefined.
   get fd() {
     return this[kInternalState].fd >= 0 ?
       this[kInternalState].fd : undefined;