EVP_PKEY_CTX_set_dh_kdf_type
if (EVP_PKEY_CTX_set_dh_kdf_type(pctx, EVP_PKEY_DH_KDF_X9_42) <= 0
if (EVP_PKEY_CTX_set_dh_kdf_type(pctx, kdf_type) <= 0)
int EVP_PKEY_CTX_set_dh_kdf_type(EVP_PKEY_CTX *ctx, int kdf);