ToggleControllers() should toggle ancestors of c.path, not c.path itself.

e.g. when c.path is like /foo/bar/baz, the following files need to be written:

• /sys/fs/cgroup/foo/cgroup.subtree_control
• /sys/fs/cgroup/foo/bar/cgroup.subtree_control

Note that /sys/fs/cgroup/foo/bar/baz/cgroup.subtree_control does not need to be written.