The 4-tuple NAT offload via PEDIT always overwrites all the 4-tuple
fields even if they had not been explicitly enabled. If any fields in
the 4-tuple are not enabled, then the hardware overwrites the
disabled fields with zeros, instead of ignoring them.

So, add a parser that can translate the enabled 4-tuple PEDIT fields
to one of the NAT mode combinations supported by the hardware and
hence avoid overwriting disabled fields to 0. Any rule with
unsupported NAT mode combination is rejected.
Signed-off-by: Herat Ramani <herat@chelsio.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>