IP fastforwarding in RELENG_4 and CURRENT/RELENG_6 (fwd)

Hello! Sorry for reposting my questions again, I hope they are interesting not only for me... What is the current status of the fast IP forwarding in RELENG_4 and in modern versions (CURRENT/RELENG_6)? I see that this code (either ip_flow.* in RELENG_4 or ip_fastfwd.c in RELENG_6) is always

IP fastforwarding in RELENG_4 and CURRENT/RELENG_6

Hello! What is the current status of the fast IP forwarding in RELENG_4 and in modern versions (CURRENT/RELENG_6)? I see that this code (either ip_flow.* in RELENG_4 or ip_fastfwd.c in RELENG_6) is always included into kernel (no separate option for it), but is disabled by default. What are dra