cake_get_tcpopt
sack_a = cake_get_tcpopt(tcph_a, TCPOPT_SACK, &oplen_a);
sack_b = cake_get_tcpopt(tcph_b, TCPOPT_SACK, &oplen_b);
ptr = cake_get_tcpopt(tcph, TCPOPT_TIMESTAMP, &opsize);