Add Q_FLAG for QDBusServiceWatcher::WatchMode.

This is needed for generic property access to work correctly.

Change-Id: I76613ace730985001fc5fe1bb1b3fa5c6a8bdf70
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/dbus/qdbusservicewatcher.h

@@ -63,6 +63,7 @@ public:
         WatchForOwnerChange = 0x03
     };
     Q_DECLARE_FLAGS(WatchMode, WatchModeFlag)
+    Q_FLAG(WatchMode)
 
     explicit QDBusServiceWatcher(QObject *parent = Q_NULLPTR);
     QDBusServiceWatcher(const QString &service, const QDBusConnection &connection,