CVE-2021-20251 lib:crypto: Add des_crypt_blob_16() for encrypting data with DES
This lets us access single-DES from Python. This function is used in a
following commit for encrypting an NT hash to obtain the verifier for a
SAMR password change.
Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz> Reviewed-by: Andreas Schneider <asn@samba.org> Reviewed-by: Andrew Bartlett <abartlet@samba.org>