`ICE_SHELF_BUOYANCY_FLUX_ITT_BUG` causes crashes

[OlgaSergienko]

A bug fix in MOM6/src/ice_shelf/MOM_ice_shelf.F90

 call get_param(param_file, mdl, "ICE_SHELF_BUOYANCY_FLUX_ITT_BUG", CS%buoy_flux_itt_bug, &
                 "Bug fix of buoyancy iteration", default=.true.)

introduced in commit 8f7cc0e causes crashes in realistic configurations. In some instances wB_flux_new is nonphysical, in some iterations do not converge.

[Hallberg-NOAA]

This issue will be addressed when PR #972 is accepted.