maximum function_stop should be 24

[jingsam]

mapbox-gl-js version:

browser:

Steps to Trigger Behavior

In style-spec, the maximum value of function_stop is 22. But the maximum zoom of mapbox-gl-js supported is 24. so I think it should be 24.

https://github.com/mapbox/mapbox-gl-js/blob/master/src/style-spec/reference/v8.json#L2320

Link to Demonstration

https://jsbin.com/

Expected Behavior

Actual Behavior