tst_QDtls: Move the function declaration outside the function

With MSVC it tries to link with the function in the scope qt::tst_QDtls::*
where it is not found

Pick-to: 6.2
Change-Id: If83a9f69c7b3834248569f6bdf203f5442693080
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

tests/auto/network/ssl/qdtls/tst_qdtls.cpp

@@ -169,6 +169,8 @@ Q_DECLARE_METATYPE(QSslKey)
 
 QT_BEGIN_NAMESPACE
 
+void qt_ForceTlsSecurityLevel();
+
 void tst_QDtls::initTestCase()
 {
     if (!TlsAux::classImplemented(QSsl::ImplementedClass::Dtls))
@@ -196,7 +198,6 @@ void tst_QDtls::initTestCase()
 
     hostName = QStringLiteral("bob.org");
 
-    void qt_ForceTlsSecurityLevel();
     qt_ForceTlsSecurityLevel();
 }