fix merging #2177 and #2169

A new method was added to the cgroup interface when #2177 was merged.

After #2177 got merged, #2169 was merged without rebase (sorry!) and compilation was failing:

  libcontainer/cgroups/fs2/fs2.go:208:22: container.Cgroup undefined (type *configs.Config has no field or method Cgroup)

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

libcontainer/cgroups/fs2/fs2.go

@@ -205,5 +205,10 @@ func (m *manager) Set(container *configs.Config) error {
 	if len(errs) > 0 && !m.rootless {
 		return errors.Errorf("error while setting cgroup v2: %+v", errs)
 	}
+	m.config = container.Cgroups
 	return nil
 }
+
+func (m *manager) GetCgroups() (*configs.Cgroup, error) {
+	return m.config, nil
+}