identification: Add support for dmdName RDN (2.5.4.54)

It's listed in RFC 2256 but was later removed with RFC 4519, but there
are still some certs that use it.

Closes strongswan/strongswan#43.

src/libstrongswan/utils/identification.h

@@ -168,6 +168,8 @@ enum id_part_t {
 	ID_PART_RDN_I,
 	/** DN Qualifier RDN of a DN */
 	ID_PART_RDN_DNQ,
+	/** dmdName RDN of a DN */
+	ID_PART_RDN_DMDN,
 	/** Pseudonym RDN of a DN */
 	ID_PART_RDN_PN,
 	/** UniqueIdentifier RDN of a DN */