Integrate stateful NAT into new flow table

[mvachhar]

[qmonnet]

By “new flow table”, I understand the one currently under review at #817 (correct me if I'm wrong).

[mvachhar]

By “new flow table”, I understand the one currently under review at #817 (correct me if I'm wrong).

Correct. There is no lookup stage or timeout stage yet though. I'm open to you writing those. We need a pipeline stage at right after lookup_dst_vpcd that attaches an Arc<FlowInfo> to the packet metadata (which means flow info has to move into its own crate, we can discuss why if you'd like) and then a stage at the end of the pipeline that calls reap_expired.