nspawn: enable all controllers we can for the "payload" subcgroup we create

In the unified hierarchy delegating controller access is safe, hence
make sure to enable all controllers for the "payload" subcgroup if we
create it, so that the container will have all controllers enabled the
nspawn service itself has.

src/basic/cgroup-util.c

@@ -2163,7 +2163,7 @@ int cg_enable_everywhere(CGroupMask supported, CGroupMask mask, const char *p) {
 
                         r = write_string_file(fs, s, 0);
                         if (r < 0)
-                                log_warning_errno(r, "Failed to enable controller %s for %s (%s): %m", n, p, fs);
+                                log_debug_errno(r, "Failed to enable controller %s for %s (%s): %m", n, p, fs);
                 }
         }