QtNetwork: code tidies: use the 4-arg connect overload

The 3-arg connect is error-prone and makes the lifetime of the
connection unclear.

Change-Id: I43dabe3d25ffc2b711aa50dec525d72a8810861c
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/network/ssl/qsslsocket.cpp

@@ -3091,10 +3091,11 @@ QTlsBackend *QSslSocketPrivate::tlsBackendInUse()
 
     tlsBackend = QTlsBackend::findBackend(activeBackendName);
     if (tlsBackend) {
-        QObject::connect(tlsBackend, &QObject::destroyed, [] {
+        QObject::connect(tlsBackend, &QObject::destroyed, tlsBackend, [] {
             const QMutexLocker locker(&backendMutex);
             tlsBackend = nullptr;
-        });
+        },
+        Qt::DirectConnection);
     }
     return tlsBackend;
 }