cgroup: always invalidate "cpu" and "cpuacct" together

This doesn't really matter, as we never invalidate cpuacct explicitly,
and there's no real reason to care for it explicitly, however it's
prettier if we always treat cpu and cpuacct as belonging together, the
same way we conisder "io" and "blkio" to belong together.

src/core/cgroup.c

@@ -2167,6 +2167,9 @@ void unit_invalidate_cgroup(Unit *u, CGroupMask m) {
         if (m & (CGROUP_MASK_IO | CGROUP_MASK_BLKIO))
                 m |= CGROUP_MASK_IO | CGROUP_MASK_BLKIO;
 
+        if (m & (CGROUP_MASK_CPU | CGROUP_MASK_CPUACCT))
+                m |= CGROUP_MASK_CPU | CGROUP_MASK_CPUACCT;
+
         if ((u->cgroup_realized_mask & m) == 0)
                 return;