#47 non-nat changing of packets

[Darren]

in some circumstances, it may be advantageous to strip ip options or tcp options from packets or replace them.
similarly, it may be worthwhile fiddling with the ip_id field in a more generic fashion than is currently possible

[Darren]

For reference, this problem needs to be solved:
http://gnats.netbsd.org/27164
... probably with defragmentation.