There's nothing built in to the current version of Mapbox that looks like it would do what you want. You might be able to get something like it by
mapView:regionDidChangeAnimated:in the map view delegate
This would probably work but it might make the view "stutter" if the user tries to scroll outside the target region. I don't know what your app does, but it might be worth considering (a) whether this is actually necessary and (b) whether there might be a better way to avoid whatever problem you expect than restricting map view scrolling.