+(*)Fix wave_speed_init mono_N2_depth bug

  Fixed a bug in which wave_speed_init was effectively discarding any values of
mono_N2_depth passed to it via the optional argument mono_N2_depth, but also
changed the default value of RESOLN_N2_FILTER_DEPTH, which was previously being
discarded, to disable the monotonization and replicate the previous results.
There were also clarifying additions made to the description how to disable
RESOLN_N2_FILTER_DEPTH.  This will change some entries in MOM_parameter_doc
files, and it will change solutions in cases that set RESOLN_N2_FILTER_DEPTH to
a non-default value and have parameter settings that use the resolution function
to scale their horizontal mixing.  There are, however, no known active
simulations where the answers are expected to change.

src/diagnostics/MOM_wave_speed.F90

@@ -39,6 +39,7 @@ module MOM_wave_speed
                                        !! wave_speed() which can be overridden by optional arguments.
   real :: mono_N2_depth = -1.          !< The depth below which N2 is limited as monotonic for the purposes of
                                        !! calculating the equivalent barotropic wave speed [Z ~> m].
+                                       !! If this parameter is negative, this limiting does not occur.
                                        !! This parameter controls the default behavior of wave_speed() which
                                        !! can be overridden by optional arguments.
   real :: min_speed2 = 0.              !< The minimum mode 1 internal wave speed squared [L2 T-2 ~> m2 s-2]
@@ -1465,7 +1466,8 @@ subroutine wave_speed_init(CS, use_ebt_mode, mono_N2_column_fraction, mono_N2_de
   call log_version(mdl, version)
 
   call wave_speed_set_param(CS, use_ebt_mode=use_ebt_mode, mono_N2_column_fraction=mono_N2_column_fraction, &
-                            better_speed_est=better_speed_est, min_speed=min_speed, wave_speed_tol=wave_speed_tol, &
+                            mono_N2_depth=mono_N2_depth, better_speed_est=better_speed_est, &
+                            min_speed=min_speed, wave_speed_tol=wave_speed_tol, &
                             remap_answers_2018=remap_answers_2018, remap_answer_date=remap_answer_date, &
                             c1_thresh=c1_thresh)
 

src/parameterizations/lateral/MOM_lateral_mixing_coeffs.F90

@@ -1239,8 +1239,9 @@ subroutine VarMix_init(Time, G, GV, US, param_file, diag, CS)
     in_use = .true.
     call get_param(param_file, mdl, "RESOLN_N2_FILTER_DEPTH", N2_filter_depth, &
                  "The depth below which N2 is monotonized to avoid stratification "//&
-                 "artifacts from altering the equivalent barotropic mode structure.",&
-                 units="m", default=2000., scale=US%m_to_Z)
+                 "artifacts from altering the equivalent barotropic mode structure.  "//&
+                 "This monotonzization is disabled if this parameter is negative.", &
+                 units="m", default=-1.0, scale=US%m_to_Z)
     allocate(CS%ebt_struct(isd:ied,jsd:jed,GV%ke), source=0.0)
   endif