ecc: Fix hard-coded value for 25519 to allow other modern curves.
* cipher/ecc.c (nist_generate_key): Support other modern curves. (test_ecdh_only_keys): Likewise. (check_secret_key): Don't use ECC_DIALECT_ED25519 for the check. (_gcry_pk_ecc_get_sexp): Support Montgomery curve.
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>