QHttpNetworkConnection: make channels member const

They are set in the ctor and should not change afterwards, so make
it explicit by making them const.

Task-number: QTBUG-102855
Change-Id: Ie1838a532f89d9cc0c3ae16521fa1829b5cdff61
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

src/network/access/qhttpnetworkconnection_p.h

@@ -212,7 +212,7 @@ public:
     // The total number of channels we reserved:
     const int channelCount;
     QTimer delayedConnectionTimer;
-    QHttpNetworkConnectionChannel *channels; // parallel connections to the server
+    QHttpNetworkConnectionChannel * const channels; // parallel connections to the server
     bool shouldEmitChannelError(QIODevice *socket);
 
     qint64 uncompressedBytesAvailable(const QHttpNetworkReply &reply) const;