Hi Roger,
If you're using Logstash for indexing data into Elasticsearch, you will need to change logstash's default index template. By default Logstash will create it's own mapping and add that to Elasticsearch. If you want to change that mapping, you will have to add some configuration to your logstash config as described here.
Here is an example of the default logtash template. You could copy that over, add the fields.limit to the settings part and then follow the instructions on the previous link on how to use it 
Hope this helps!