Should be able to export and import flowtable state during migration

[FelixMcFelix]

During live instance migration, we currently setup an identical OPTE port on the new sled with regard to firewall rules, external IPs, etc. However this loses several pieces of stateful information currently encoded in the flowtable:

• Stateful firewall entries needed for pairwise allow,
• Temporary port allocations for SNAT'd flows,
• External IP affinity for each flow.

Some of these can be regenerated depending on how hosts behave, but otherwise these will impact VPC-external traffic. To minimise this, we want to ideally carry this state over to the new sled once execution stops.