KPP low level interface handles arrays > nlev+1

The cvmix_coeffs_kpp_low routine needs nlev and max_nlev as inputs: nlev is the
number of [active] levels in the column, and max_nlev is the size of the arrays
being passed (if column has 60 levels but the ocean bottom is level 15, then
nlev = 15 prevents CVMix from doing any computation below the ocean bottom and
max_nlev = 60 allows CVMix to handle memory correctly).