core/cgroup: make unit_has_host_root_cgroup take const Unit*

(cherry picked from commit 4442aef08e0fe8ba381b580455f7eb281c5a28a1)
(cherry picked from commit 06c2ee39799064a82d2af1bee7a5c72ebdd66090)

src/core/cgroup.c

@@ -100,8 +100,9 @@ bool unit_has_startup_cgroup_constraints(Unit *u) {
                c->startup_memory_low_set;
 }
 
-bool unit_has_host_root_cgroup(Unit *u) {
+bool unit_has_host_root_cgroup(const Unit *u) {
         assert(u);
+        assert(u->manager);
 
         /* Returns whether this unit manages the root cgroup. This will return true if this unit is the root slice and
          * the manager manages the root cgroup. */

src/core/cgroup.h

@@ -389,7 +389,7 @@ int unit_reset_accounting(Unit *u);
         })
 
 bool manager_owns_host_root_cgroup(Manager *m);
-bool unit_has_host_root_cgroup(Unit *u);
+bool unit_has_host_root_cgroup(const Unit *u);
 
 bool unit_has_startup_cgroup_constraints(Unit *u);