ipfw forward in cooperative mode with pf

[Franco Fichtner]

Hi,

I'm working on making pf and ipfw work more closely together
in the pfil hooks.  This requires pf making use of the
PACKET_TAG_IPFOWARD as a second caller, but ipfw code needs
to be tightened slightly in order to make it cooperative:

https://reviews.freebsd.org/D8109

The grand scheme of things is that using pf -> ipfw in the
pfil in hook makes pf blackhole packets when using route-to
and friends, because pf skips ahead to if_output with code
copied from ip_output().  The packets never arrive in ipfw,
where they can't be forwarded (or even dropped).

I don't have a reviewer / committer for this at the moment,
so all help and questions are welcome.


Cheers,
Franco