Fixes #6444 - add support for virtual NICs

> @ares are we on purpose keeping the odd nested-attributes format just to avoid updating the JS/form?

yes, since we use nested attributes for interfaces and we're submitting the same form to this action, we have to parse  this structure, otherwise we'd have to change not only the form but the whole logic around host saving

> would this work on update too?

no, but we don't allow changing interface type once it's created, we can't convert BMC to Interface. It's easy to remove interface and create new one in the form, it's just JS so I don't think we need to support updating