Add two new fields to portmapperapi.PortBinding: NAT and Forwarding.
These can be used by portmappers to specify how they want their callers
(e.g. bridge driver) to reconfigure the host firewall to NAT a host
port, or allow forwarding to the container port.
If portmappers don't want to opt-in to these, they can implement their
own firewall rules, and not fill these fields.
Signed-off-by: Albin Kerouanton <albinker@gmail.com>
The two unexported fields of portBindingReq (ChildHostIP and DisableNAT)
are temporarily exported. DisableNAT will be replaced in a future commit
by a 'Mapper' field indicating which portmapper should be used (e.g.
'nat' or 'routed').
Signed-off-by: Albin Kerouanton <albinker@gmail.com>
