Retiring src/sys/netiso and associated code

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

Hi all,
a while ago the OSI options were removed from most default kernel
configurations due to questionable security state of the code and
general lack of testing. I don't think the situation has improved in any
noticable way. It adds complexity for the routing code, which I want to
work on. Not breaking it requires testing, which doesn't seem to happen.
So who is actively using the OSI network stack with NetBSD and is in a
position to test changes? Alternatively, I would like to finally let it
rest in peace.

Joerg