nfp: flower-ct: make a full copy of the rule when it is a NFT flow

The nft flow will be destroyed after offload cb returns. This means
we need save a full copy of it since it can be referenced through
other paths other than just the offload cb, for example when a new
pre_ct or post_ct entry is added, and it needs to be merged with
an existing nft entry.

Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
Signed-off-by: Louis Peens <louis.peens@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>