Kea DHCPv4 not able to send vendor options if client doesn't send vivso

A customer reported a problem that Kea is unable to send back vivso sub-options. Kea sends only the top-level vivso option with correct vendor-id, but is not able to send back any sub-options.

The problem has been investigated and this is caused by the Genexis clients that do not send vivso option itself. That way, the server is not able to figure out what vendor-id to use.

In ideal world, Genexis client would send vivso with enterprise value set to 25167. But they don't and we need to tweak Kea to be able to work around that.