SLH_WOTS_LEN2
#define SLH_WOTS_CHECKSUM_LEN ((SLH_WOTS_LEN2 + SLH_WOTS_LOGW + 7) / 8)
size_t len = len1 + SLH_WOTS_LEN2; /* 2 * n + 3 (3 checksum nibbles) */
size_t len = len1 + SLH_WOTS_LEN2; /* 2n + 3 */