title: Datatable disable search option searchable not working
body: <p>Here is my code, I'm trying to disable search on all column except one on global search.
  This always search for the primary key I have defined. Using the datatable example server side class.</p>
  
  <pre><code>var datatable = $('#datatable').DataTable({
          "ajax": "/get_data/",
          "processing": true,
          "serverSide": true,
          "deferRender": true,
  
          "columns": [
              {"searchable": false, "data": "id"},
              {"searchable": false, "data": "user_id"},
              {"searchable": true, "data": "bl_number"},
              {"searchable": false, "data": "invoice_number"},
              {"searchable": false, "data": "ship_date"},
              {"searchable": false, "data": "eta_date"},
              {"searchable": false, "data": "vessel"},
              {"searchable": false, "data": "port_of_load"},
              {"searchable": false, "data": "port_of_discharge"},
              {"searchable": false, "data": "containers"},
              {"searchable": false, "data": "status"}
          ],
  
          "initComplete": function(settings, json) {
              $(this).show();
          }
      });
  
      datatable.on('click', '.btn-edit', function(){
          var data = datatable.row($(this).closest('tr')).data();
          edit(data);
      });
  </code></pre>
  
  <p>If I use array instead of json object I could use the following code and it works fine. But I need to work with Json objects not array.</p>
  
  <pre><code>var datatable = $('#datatable').DataTable({
      "ajax": "/get_data/",
      "processing": true,
      "serverSide": true,
      "deferRender": true,
  
      "columnDefs": [ 
          {
              "targets": 0,
              "render": function ( data, type, full, meta ) {
                  return '&lt;a href="javascript:;" class="btn-edit"&gt;Edit&lt;/a&gt;';
              }
          },
          { targets: 1, searchable: true },
          { targets: '_all', searchable: false }
      ]
  });
  
  datatable.on('click', '.btn-edit', function(){
      var data = datatable.row($(this).closest('tr')).data();
      edit(data);
  });
  </code></pre>