[Qt] allow setting listen via GUI

- add DEFAULT_LISTEN in net.h and use in the code (shared
  setting between core and GUI)

Important: This makes it obvious, that we need to re-think the
settings/options handling, as GUI settings are processed before
any parameter-interaction (which is mostly important for network
stuff) in AppInit2()!

src/qt/forms/optionsdialog.ui

@@ -242,6 +242,16 @@
          </property>
         </widget>
        </item>
+       <item>
+        <widget class="QCheckBox" name="allowIncoming">
+         <property name="toolTip">
+          <string>Accept connections from outside</string>
+         </property>
+         <property name="text">
+          <string>Allow incoming connections</string>
+         </property>
+        </widget>
+       </item>
        <item>
         <widget class="QCheckBox" name="connectSocks">
          <property name="toolTip">

src/qt/optionsdialog.cpp

@@ -151,6 +151,7 @@ void OptionsDialog::setModel(OptionsModel *model)
     /* Wallet */
     connect(ui->spendZeroConfChange, SIGNAL(clicked(bool)), this, SLOT(showRestartWarning()));
     /* Network */
+    connect(ui->allowIncoming, SIGNAL(clicked(bool)), this, SLOT(showRestartWarning()));
     connect(ui->connectSocks, SIGNAL(clicked(bool)), this, SLOT(showRestartWarning()));
     /* Display */
     connect(ui->lang, SIGNAL(valueChanged()), this, SLOT(showRestartWarning()));
@@ -171,6 +172,7 @@ void OptionsDialog::setMapper()
 
     /* Network */
     mapper->addMapping(ui->mapPortUpnp, OptionsModel::MapPortUPnP);
+    mapper->addMapping(ui->allowIncoming, OptionsModel::Listen);
 
     mapper->addMapping(ui->connectSocks, OptionsModel::ProxyUse);
     mapper->addMapping(ui->proxyIp, OptionsModel::ProxyIP);

src/qt/optionsmodel.cpp

@@ -110,6 +110,11 @@ void OptionsModel::Init()
     if (!SoftSetBoolArg("-upnp", settings.value("fUseUPnP").toBool()))
         addOverriddenOption("-upnp");
 
+    if (!settings.contains("fListen"))
+        settings.setValue("fListen", DEFAULT_LISTEN);
+    if (!SoftSetBoolArg("-listen", settings.value("fListen").toBool()))
+        addOverriddenOption("-listen");
+
     if (!settings.contains("fUseProxy"))
         settings.setValue("fUseProxy", false);
     if (!settings.contains("addrProxy"))
@@ -214,6 +219,8 @@ QVariant OptionsModel::data(const QModelIndex & index, int role) const
             return settings.value("nDatabaseCache");
         case ThreadsScriptVerif:
             return settings.value("nThreadsScriptVerif");
+        case Listen:
+            return settings.value("fListen");
         default:
             return QVariant();
         }
@@ -339,6 +346,12 @@ bool OptionsModel::setData(const QModelIndex & index, const QVariant & value, in
                 setRestartRequired(true);
             }
             break;
+        case Listen:
+            if (settings.value("fListen") != value) {
+                settings.setValue("fListen", value);
+                setRestartRequired(true);
+            }
+            break;
         default:
             break;
         }

src/qt/optionsmodel.h

@@ -42,6 +42,7 @@ public:
         ThreadsScriptVerif,     // int
         DatabaseCache,          // int
         SpendZeroConfChange,    // bool
+        Listen,                 // bool
         OptionIDRowCount,
     };