OSSL_CMP_ATAV_push1
ok = OSSL_CMP_ATAV_push1(&keyspec, eckeyalg)
&& OSSL_CMP_ATAV_push1(&keyspec, rsakeylen);
OSSL_CMP_ATAV_push1(keySpec, atav);
int OSSL_CMP_ATAV_push1(OSSL_CMP_ATAVS **sk_p, const OSSL_CMP_ATAV *atav);