Commit b95b6ba1a2959e2294a8848fa35f20163388eb06 changed package_ipk.bbclass
to xz when building packages. This updates OpkgDpkgPM.extract() accordingly.
(From OE-Core rev: c09a22c421a57701f6b943eb50b9bae1545e5b39)
Signed-off-by: Angus Lees <gus@inodes.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>