How to patch the kernel?

[Lyle Scott III]

I don't have much experience patching anything, really.

I was told by the port security/ipsec-tools to patch the kernel if i wanted
to use nat-transversals.

they provide me with
http://vanhu.free.fr/FreeBSD/patch-natt-freebsd6-2007-05-31.diff, but I am
now sure how to patch up the kernel so I can do a buildworld.

Any help would be much appreciated.  I took a quick read over the patch
manpage, but simply 'patch < file' in /usr/src askes me what file to
patch...

This is on freebsd 6.2-release-p9 BTW.  thanks

-- 
Lyle Scott, III
http://www.lylescott.ws