- md6: make sure (*compression_hook) vector is instantiated.
- md6: make sure (*compression_hook) vector is instantiated.

devzero2000/RPM5,devzero2000/RPM5,devzero2000/RPM5,devzero2000/RPM5,devzero2000/RPM5,devzero2000/RPM5,devzero2000/RPM5