We *must not* assume that an entry returned by KDBUS_CMD_LIST only
carries a single KDBUS_ITEM_OWNED_NAME. Similarly, we already parse
multiple such items for message-metadata, so make sure we support the
same on KDBUS_CMD_LIST.
By relying on the kernel to return all names separately, we limit the
kernel API significantly. Stop this and let the kernel decide how to
return its data.