tcp_dooptions
tcp_dooptions(&to, (void *)(th + 1),
tcp_dooptions(&to, optp, optlen, 0);
tcp_dooptions(&to, optp, optlen, TO_SYN);
tcp_dooptions(&to, optp, optlen, thflags);
tcp_dooptions(&to, (u_char *)(th + 1),
tcp_dooptions(&to, optp, optlen,
tcp_dooptions(&to, (u_char *)(th + 1),
tcp_dooptions(&to, (u_char *)(th + 1),
void tcp_dooptions(struct tcpopt *, u_char *, int, int);