TCP_MAX_COMBINED_HEADER_LENGTH
assert(tcp->tcp_iphc_len >= TCP_MAX_COMBINED_HEADER_LENGTH);
tcp->tcp_iphc_len = TCP_MAX_COMBINED_HEADER_LENGTH;
#define TCP_MAX_LSO_LENGTH (IP_MAXPACKET - TCP_MAX_COMBINED_HEADER_LENGTH)
TCP_MAX_COMBINED_HEADER_LENGTH