Fix DH gettable OSSL_PKEY_PARAM_DH_PRIV_LEN so that it has the correct type.
Fix DH gettable OSSL_PKEY_PARAM_DH_PRIV_LEN so that it has the correct
type.

Reviewed-by: Paul Dale <ddec78389666b4f7c9b4d110380c848489a3e4aa@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14564)

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl