build directory, especially those for other operating systems.
The kernel module shims for other operating systems are hereby removed.
The kernel module shim for FreeBSD, mlfk_ipl.c, is already in
sys/contrib/ipfilter/netinet. The one here is never used and should
not be in the userland build directory either.
mlfk_rule.c isn't used either however we will keep it in case someone
wishes to use this shim to load rules via a kernel module, handy for
embedded. In that case it should be copied to
sys/contrib/ipfilter/netinet and a Makefile created to employ it.
(Probably a useful documentation project when time permits.)
MFC after: 1 month
e9a5006bff