CAMBparams_SetNeutrinoHierarchyBase(this, omnuh2, omnuh2_sterile, nnu, standard_neutrino_neff, neutrino_hierarchy, num_massive_neutrinos)
Set neutrino hierarchy in the approximate two-eigenstate model (treating two as exactly degenerate,
and assuming non-relativistic),
or use degenerate mass approximation.
omnuh2 is the massive total neutrino density today, omnuh2_sterile is the component of that due to steriles
omnuh2_sterile is interpreted as in the Planck parameter papers