Flat network support is broken

[fw2568]

Flat networks don't work any more in following situations:

• multiple network adapters (overlay and another one in a flat network), project sync fails with Environment default: Subnet default not found in network [FLAT NETWORK NAME]

• Updating catlet from overlay to flat network causes a DB constraint error on MAC address : SQLite Error 19: 'UNIQUE constraint failed: NetworkPorts.MacAddress'

Reproduce steps:

1. create a provider network config with both a overlay network and a flat network
2. create a catlet with overlay network
3. switch network to flat network and / or add flat network as second network.

AB#716

[fw2568]

This issue breaks also Get-Catlet, due to a mapping error:

Mapping types: SelectListIterator2 -> IEnumerable1 System.Linq.Enumerable+SelectListIterator2[[Eryph.StateDb.Model.CatletNetworkPort, Eryph.StateDb, Version=0.1.0.0, Culture=neutral, PublicKeyToken=null],[System.ValueTuple2[[Eryph.StateDb.Model.Catlet, Eryph.StateDb, Version=0.1.0.0, Culture=neutral, PublicKeyToken=null],[Eryph.StateDb.Model.CatletNetworkPort, Eryph.StateDb, Version=0.1.0.0, Culture=neutral, PublicKeyToken=null]], System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]] -> System.Collections.Generic.IEnumerable`1[[Eryph.Modules.ComputeApi.Model.V1.CatletNetwork, Eryph.Modules.ComputeApi, Version=0.1.0.0, Culture=neutral, PublicKeyToken=null]] ---> System.NullReferenceException: Object reference not set to an instance of an object.