As part of the general cleanup of the ipfilter code, special cases

As part of the general cleanup of the ipfilter code, special cases
are committed separately to document fixing them separately from
the general cleanup. In this case we don't want to hide the utter
brokenness of what is being fixed.

Clean up a discombobulated block of #if's, with one block unreachable.
ip_fil.c is used in ipftest which is used to dry-run test ipfilter
rules in userspace without loading them in the kernel. The call to
(*ifp->if_output) matches that in the FreeBSD kernel.

Further testing and work will be required to make ipftest fully
functional.

MFC after:	1 week