Always copy the request metadata.

This is necessary because the HTTP/1.1 machinery will recycle the
Metadata.Request object, and it may race with a thread dispatch to
the HTTP/2 machinery that will handle the request.

jetty-http2/http2-server/src/main/java/org/eclipse/jetty/http2/server/HTTP2ServerConnection.java

@@ -189,7 +189,7 @@ public class HTTP2ServerConnection extends HTTP2Connection implements Connection
             upgradeFrames.add(new PrefaceFrame());
             upgradeFrames.add(settingsFrame);
             // Remember the request to send a response from onOpen().
-            upgradeFrames.add(new HeadersFrame(1, request, null, true));
+            upgradeFrames.add(new HeadersFrame(1, new Request(request), null, true));
         }
         return true;
     }