MBUF_PEXT_TRAIL_LEN
KASSERT(tls->params.tls_tlen <= MBUF_PEXT_TRAIL_LEN,
trail_len + hdr_len <= MBUF_PEXT_TRAIL_LEN) {
(MBUF_PEXT_MAX_PGS * PAGE_SIZE + MBUF_PEXT_HDR_LEN + MBUF_PEXT_TRAIL_LEN)
char extpg_trail[MBUF_PEXT_TRAIL_LEN];