IP_ADJCKSUM_PARTIAL
IP_ADJCKSUM_PARTIAL(mp->b_rptr + DB_CKSUMSTART(mp),
IP_ADJCKSUM_PARTIAL(mp->b_rptr + DB_CKSUMSTART(mp),
IP_ADJCKSUM_PARTIAL(cksum_start, mp, mp1, len, adj);
IP_ADJCKSUM_PARTIAL(cksum_start, mp, mp1, len, adj);