about net.inet.ip.fw.default_to_accept sysctl OID in generic-kernel builds

[subbsd]

Hello maillist

In my custom kernel with IPFIREWALL_DEFAULT_TO_ACCEPT, this OID 
(net.inet.ip.fw.default_to_accept) is present in system and i can control him 
in loader.conf.  I see OID when sysctl(8) execute and when i looks in binary 
kernel or ipfw.ko:

% strings /boot/kernel/ipfw.ko /boot/kernel/kernel | grep 
net.inet.ip.fw.default_to_accept

net.inet.ip.fw.default_to_accept
net.inet.ip.fw.default_to_accept

(it presents in ipfw.ko and kernel)

But ipfw.ko from GENERIC kernel does not produce this OID so, booting machine 
on GENERIC kernel with FIREWALL and "65535 pass ip from any to any" is not 
possible.

In /usr/src/sys/netinet/ipfw/ip_fw2.c

i see:

#ifdef SYSCTL_NODE
...
SYSCTL_INT(_net_inet_ip_fw, OID_AUTO, default_to_accept, CTLFLAG_RDTUN,
    &default_to_accept, 0, "Make the default rule accept all packets.");
TUNABLE_INT("net.inet.ip.fw.default_to_accept", &default_to_accept);
#endif /* SYSCTL_NODE */


What is SYSCTL_NODE  and why net.inet.ip.fw.default_to_accept not producing in 
ipfw.ko without IPFIREWALL_DEFAULT_TO_ACCEPT ? 

Thanks.