This is one of:
 http://www.berklix.com/~jhs/src/bsd/fixes/FreeBSD/src/gen/sys/\
  netinet/ip_fw2.c.REL=5.5-RELEASE.diff
  netinet/ip_fw2.c.REL=7.4-RELEASE.diff
  netinet/ipfw/ip_fw2.c.REL=8.4-RELEASE.diff
  netpfil/ipfw/ip_fw2.c.REL=9.2-RELEASE.diff
  netpfil/ipfw/ip_fw2.c.REL=12.1-RELEASE.diff
  netpfil/ipfw/ip_fw2.c.REL=CURRENT.diff

 5.5 netinet/ip_fw2.c		autoinc_step = 100
 6.4 netinet/ip_fw2.c:		autoinc_step = 100
 7.4 netinet/ip_fw2.c:		autoinc_step = 100
 8.0 netinet/ipfw/ip_fw2.c:
 8.4 netinet/ipfw/ip_fw2.c:	V_autoinc_step = 100
 9.2 netpfil/ipfw/ip_fw2.c:	V_autoinc_step = 100
12.2 netpfil/ipfw/ip_fw2.c:	V_autoinc_step = 100

*** 5.2-RELEASE/src/sys/netinet/ip_fw2.c	Tue Dec 23 13:25:56 2003
--- gen/src/sys/netinet/ip_fw2.c	Wed Jan 28 12:33:16 2004
***************
*** 131,137 ****
  MALLOC_DEFINE(M_IPFW, "IpFw/IpAcct", "IpFw/IpAcct chain's");
  
  static int fw_debug = 1;
! static int autoinc_step = 100; /* bounded to 1..1000 in add_rule() */
  
  #ifdef SYSCTL_NODE
  SYSCTL_NODE(_net_inet_ip, OID_AUTO, fw, CTLFLAG_RW, 0, "Firewall");
--- 131,137 ----
  MALLOC_DEFINE(M_IPFW, "IpFw/IpAcct", "IpFw/IpAcct chain's");
  
  static int fw_debug = 1;
! static int autoinc_step = 20; /* bounded to 1..1000 in add_rule() */
  
  #ifdef SYSCTL_NODE
  SYSCTL_NODE(_net_inet_ip, OID_AUTO, fw, CTLFLAG_RW, 0, "Firewall");