qml: expose bolt11_fallback in preferences

electrum/gui/qml/components/Preferences.qml

@@ -222,6 +222,17 @@ Pane {
                                     Config.useGossip = currentValue == 'gossip'
                             }
                         }
+
+                        Switch {
+                            id: useFallbackAddress
+                            text: qsTr('Use onchain fallback address for Lightning invoices')
+                            Layout.columnSpan: 2
+                            onCheckedChanged: {
+                                if (activeFocus)
+                                    Config.useFallbackAddress = checked
+                            }
+                        }
+
                     }
 
                 }
@@ -275,6 +286,7 @@ Pane {
         fiatEnable.checked = Daemon.fx.enabled
         spendUnconfirmed.checked = Config.spendUnconfirmed
         lnRoutingType.currentIndex = Config.useGossip ? 0 : 1
+        useFallbackAddress.checked = Config.useFallbackAddress
 
         var plugins = AppController.plugins
         for (var i=0; i<plugins.length; i++) {

electrum/gui/qml/qeconfig.py

@@ -120,6 +120,16 @@ class QEConfig(AuthMixin, QObject):
         self.config.set_key('use_gossip', gossip)
         self.useGossipChanged.emit()
 
+    useFallbackAddressChanged = pyqtSignal()
+    @pyqtProperty(bool, notify=useFallbackAddressChanged)
+    def useFallbackAddress(self):
+        return self.config.get('bolt11_fallback', True)
+
+    @useFallbackAddress.setter
+    def useFallbackAddress(self, use_fallback):
+        self.config.set_key('bolt11_fallback', use_fallback)
+        self.useFallbackAddressChanged.emit()
+
     @pyqtSlot('qint64', result=str)
     @pyqtSlot('qint64', bool, result=str)
     @pyqtSlot(QEAmount, result=str)