cgroup: in unit_invalidate_cgroup() actually modify invalidation mask

cgroup: in unit_invalidate_cgroup() actually modify invalidation mask

Previously this would manipulate the realization mask for invalidating
the realization. This is a bit ugly though as the realization mask's
primary purpose to is to reflect in which hierarchies a cgroup currently
exists, and it's probably a good idea to keep that in sync with
realities.

We nowadays have the an explicit fields for invalidating cgroup
controller information, the "cgroup_invalidated_mask", let's use this
one instead.

The effect is pretty much the same, as the main consumer of these masks
(unit_has_mask_realize()) checks both anyway.