Fix sip bindings

python/gui/qgsfieldmodel.sip

@@ -21,6 +21,14 @@ class QgsFieldModel : QAbstractItemModel
       ExpressionValidityRole, /*!< return if expression is valid or not */
       FieldTypeRole /*!< return the field type (if a field, return QVariant if expression) */
     };
+    /**
+     * Filters for which fields should be shown
+     */
+    enum Filter
+    {
+      WritableFields = 1 //!< Only show writable fields
+    };
+    typedef QFlags<QgsFieldModel::Filter> Filters;
 
     /**
      * @brief QgsFieldModel creates a model to display the fields of a given layer