message: tcp_defer_accept option support for FreeBSD.
  SO_ACCEPTFILER acts similarly as Linux's TCP_DEFER_ACCEPT.
diff: @@ -166,6 +166,17 @@ int ListenPort::listen() {
  }
  #endif
  +#ifdef SO_ACCEPTFILTER
  + if (tcp_defer_accept) {
  + struct accept_filter_arg a;
  + memset(&a, 0, sizeof(a));
  + strcpy(a.af_name, "httpready");
  + if (socket->set_option(SOL_SOCKET, SO_ACCEPTFILTER, &a, sizeof(a)) != 0) {
  + swSysWarn("setsockopt(SO_ACCEPTFILTER) failed");
  + }
  + }
  +#endif
  +
  #ifdef TCP_FASTOPEN
  if (tcp_fastopen) {
  if (socket->set_option(IPPROTO_TCP, TCP_FASTOPEN, tcp_fastopen) != 0) {
  