title: Custom data source property dataSrc and pagination issue
body: <p>I'm working with jQuery DataTables and server-side processing mode. But I'm facing an issue with data table, I've search every thing in Datatables documentation but couldn't find my answer.</p>
  
  <p>So the problem is I'm getting response from server as JSON like this:</p>
  
  <p><a href="https://i.stack.imgur.com/sYkx7.png" rel="noreferrer"><img src="https://i.stack.imgur.com/sYkx7.png" alt="JSON response"></a></p>
  
  <p>As you can see in this JSON response, datatables required JSON is in <code>data.data</code> to set this data source in datatables there is a property which is <a href="https://datatables.net/examples/ajax/custom_data_property.html" rel="noreferrer">Custom Data Property</a> and it working fine and shows the rows. Now problem is that datatables is not considering pagination parameters from JSON which is why it show's this:</p>
  
  <p><a href="https://i.stack.imgur.com/eGlNg.png" rel="noreferrer"><img src="https://i.stack.imgur.com/eGlNg.png" alt="Pagination"></a></p>
  
  <p>Please note that I cannot change JSON response from server side.</p>
  
  <p><strong>Update:</strong>
  Here is js call script:</p>
  
  <pre><code>$(document).ready(function () {
     $("#example").dataTable({
        "ajax": {
            url: app.getApiUrlWithAccessToken('lead/get_all'),
            dataSrc: function(json){
                return json.data.data;
            }
        },
        "lengthMenu": [1,2,5,10,15],
        "columns": [
            { "data": "first_name" },
            { "data": "last_name" },
            { "data": "title" },
            { "data": "email" },
            { "data": "city" },
            { "data": "status" }
        ],
        "processing": true,
        "serverSide": true
     });
  });
  </code></pre>