Undocumented <admin-interface> handling of name and hwaddr interface is confusing

[ydirson]

parseInterface() code is as follows:

        if_name = getStrAttribute(node, ['name'])
        if if_name and if_name in nethw:
            if_hwaddr = nethw[if_name].hwaddr
        else:
            if_hwaddr = getStrAttribute(node, ['hwaddr'])
            if if_hwaddr:
                matching_list = filter(lambda x: x.hwaddr == if_hwaddr.lower(), nethw.values())
                if len(matching_list) == 1:
                    if_name = matching_list[0].name
        if not if_name and not if_hwaddr:
             raise AnswerfileException("<admin-interface> tag must have one of 'name' or 'hwaddr'")

It is allowed to specify both name and hwaddr, in which case

• if name points to an existing interface, hwaddr is ignored
• if not, name is ignored

If any or both are specified, but do not match the hardware, the message says they are missing.

We should likely ensure exactly one is given, and issue more specific error messages.