[qtbase] Improved online state handling. Contributes to JB#34613

Particularly, it handles the following scenario:

1. Session state changes from Connected to Connecting
   (that could be another bug but why not?)
2. _q_networkSessionStateChanged switches online to false
3. Session state changes to Disconnected, online is already false
4. online state stays false even though another configuration
   gets connected.

With this change, when one session becomes Disconnected, a new
session is created and online state becomes true as it should.

src/network/access/qnetworkaccessmanager.cpp

@@ -1617,7 +1617,7 @@ void QNetworkAccessManagerPrivate::_q_networkSessionStateChanged(QNetworkSession
         emit q->networkSessionConnected();
     lastSessionState = state;
 
-    if (online && state == QNetworkSession::Disconnected) {
+    if (state == QNetworkSession::Disconnected) {
         Q_FOREACH (const QNetworkConfiguration &cfg, networkConfigurationManager.allConfigurations()) {
             if (cfg.state().testFlag(QNetworkConfiguration::Active)) {
                 reallyOnline = true;