When using new network, the tests use an IPv6-based localhost address for binding and connecting.

The local socket is opened in `setUp`: ```Smalltalk setUp

listenerSocket := Socket newTCP listenOn: self listenerPort backlogSize: 4 interface: self listenerAddress. ```

The `listenerAddress` is derived as follows: ```Smalltalk ^ NetNameResolver addressForName: 'localhost' ``` In `oldNetwork`, that's an IPv4, in `!oldNetwork` that's an IPv6. _this is good_

However, the _Socket_ is created as `newTCP`, that is, _explicitely IPv4_: ```Smalltalk newTCP "Create a socket and initialise it for TCP" ^self newTCP: SocketAddressInformation addressFamilyINET4 ``` This is bad. This is where the Error message comes from.

This should be changed to use the address familty that fits best to the current old/new-network.

On top of that, `#listenOn:backlogSize: interface:` *solely* deals with IPv4 adresses.

The correct way is to use the indirection of `SocketAddressInformation` in `#listenWithBacklog:`. This deals correctly with the address family.

Things to do: - [ ] fix the test setup to use the SAI info and/or discriminate old/new network - [ ] maybe Bail in the socket plugin earlier when a new-network socket is used in old-network-ipv4-only code.

wait, this is fixed?

Reopened #428.