PR kern/117234 - ipfw + ipv6 tcp acks

[Ivan Voras]

Hi,

Can someone please review and if possible commit this PR:

http://www.freebsd.org/cgi/query-pr.cgi?pr=117234

There are multiple versions of the patch in the PR, there is none for 
-CURRENT.

The problem is that, for ipv4, ipfw sends keepalives for TCP connections 
handled by dynamic rules, while on ipv6 the dynamic rules simply expire 
after a timeout, causing connections to be broken in a bad way 
(established TCP packets simply get dropped).

I don't know if the patch is the correct way to solve the problem, but 
it apparently works.