title: Aggrid params sortModel undefined
body: <p>Hi i am trying to generalize my data source for multiple tables.
  I am using datasource below and to do what i want i expect aggrid to pass sortModel as <code>params: IGetRowsParams</code> but aggrid doesnt update sort model. If i get sortModel directly from api i get correct sort model. I am using infinite row model.</p>
  <pre class="lang-js prettyprint-override"><code>function createDatasource() {
    return {
      rowCount: null,
      getRows: (params: IGetRowsParams) =&gt; {
        const sortModel = this.gridOptions.api.getSortModel();
        const paramsSortModel = params.sortModel 
      }
    }
  }
  </code></pre>