Description of problem:
-----------------------------
3 ODL Controllers and 2 Compute nodes.

Create an external-flat-network, router and vxlan tenant network.
Associate the router to the external-network and tenant subnet.
Spawn couple of VMs and associate FIPs to each of the VMs.

Take down the compute nodes, start them again and create new VMs, assign FIPs and try to reach them

How reproducible:
Random

Observations:
-------------
The reason why some of the flows were missing for FIP/SNAT is that an invalid dpnId (i.e., 0) was selected as an NAPT Switch.
Ideally a dpnId of zero should not be configured as an NAPT switch in the router-to-napt-switch models and the missing flows are only a side-effect of this.

{
"napt-switches": {
"router-to-napt-switch": [

]
}
}