Apply by doing:
	cd /usr/src
	patch -p0 < 006_nat-t.patch

And then rebuild and install isakmpd:
	cd sbin/isakmpd
	make obj
	make depend
	make && make install

Index: sbin/isakmpd/nat_traversal.c
===================================================================
RCS file: /cvs/src/sbin/isakmpd/nat_traversal.c,v
retrieving revision 1.10
diff -u -p -r1.10 nat_traversal.c
--- sbin/isakmpd/nat_traversal.c	5 Mar 2005 12:22:40 -0000	1.10
+++ sbin/isakmpd/nat_traversal.c	5 Nov 2005 21:37:37 -0000
@@ -58,8 +58,7 @@
  */
 static const char *isakmp_nat_t_cap_text[] = {
 	"draft-ietf-ipsec-nat-t-ike-02\n",	/* draft, V2 */
-	"draft-ietf-ipsec-nat-t-ike-03",	/* draft, V3 */
-	"RFC 3947"
+	"draft-ietf-ipsec-nat-t-ike-03"		/* draft, V3 */
 };
 
 /* In seconds. Recommended in draft-ietf-ipsec-udp-encaps-09.  */