UPDATE, this patch is not going to work properly, so forget the cricket!!!
Yesterday I've rewrote patch to natd using kqueue. Since I do not have FreeBSD with nat around, patch is not tested yet. Probably tomorrow will be chance to test. Long story- short. Testers are welcome. No warranty!!!
How to apply this patch:
(at this point you should already have the system sources)
cd /usr/src/sbin/natd &&amp; patch -p2 < /path/to/natd.patch && make && make install clean