hash: add XCBCMAC

XCBC-MAC is often used in ipsec. The only difference with CMAC is the
way to compute subkeys (RFC 3566 section 4).

I added self tests with test vectors provided in RFC 3566 Section 4.6

See http://tools.ietf.org/html/rfc3566

Signed-off-by: Robin Jarry <robin.jarry@6wind.com>