In 8.0-RELEASE it becomes sys/netinet/ipfw/ip_fw2.c
	I've hacked this, based on ../ip_fw2.c.REL=7.2-RELEASE.diff 
	but not thought the code through.
*** 8.1-RC2/src/sys/netinet/ipfw/ip_fw2.c	Sat Jul 17 12:05:18 2010
--- new-generic/src/sys/netinet/ipfw/t	Sat Jul 17 17:45:35 2010
***************
*** 2305,2311 ****
  	chain = &V_layer3_chain;
  
  	/* First set up some values that are compile time options */
! 	V_autoinc_step = 100;	/* bounded to 1..1000 in add_rule() */
  	V_fw_deny_unknown_exthdrs = 1;
  #ifdef IPFIREWALL_VERBOSE
  	V_fw_verbose = 1;
--- 2305,2311 ----
  	chain = &V_layer3_chain;
  
  	/* First set up some values that are compile time options */
! 	V_autoinc_step = 20;	/* bounded to 1..1000 in add_rule() */
  	V_fw_deny_unknown_exthdrs = 1;
  #ifdef IPFIREWALL_VERBOSE
  	V_fw_verbose = 1;