Inconsistency in use of max_nlev

[vanroekel]

A few functions within the CVMix KPP interface take the argument max_nlev to allow KPP to be computed over a subset of the entire column (e.g. cvmix_coeffs_kpp).

1. This option should be available to all routines (e.g. compute_turbulent_scales, compute_bulk_richardson).

2. Even when the max_nlev option is included in a routine, there are portions of that routine that still compute over nlevs For example, within coeffs_kpp, compute_turbulent_scales is called it is over nlevs (determined by the size of zw_ctr). Thus, if max_nlev != nlevs and all of zw_ctr is sent, an issue can arise.