DTLS server - use the proper TLS configuration

The one we had before was invalid and we ended up with
defaultDtlsConfiguration which has peerVerifyMode == AutoVerify.

Change-Id: I5b9ceb027e90189325c1d8fd0db37d1b212ebbc8
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

examples/network/secureudpserver/server.cpp

@@ -92,6 +92,7 @@ DtlsServer::DtlsServer()
 {
     connect(&serverSocket, &QAbstractSocket::readyRead, this, &DtlsServer::readyRead);
 
+    serverConfiguration = QSslConfiguration::defaultDtlsConfiguration();
     serverConfiguration.setPreSharedKeyIdentityHint("Qt DTLS example server");
     serverConfiguration.setPeerVerifyMode(QSslSocket::VerifyNone);
 }