The comment is misleading. This function checks, if the IP address on the interface is singular enough to add an additional loopback route for the local host in the attached network,
Of course, all excluded cases do need a loopback route, too. But not an extra one,
Indeed, there is a clash for the "loopback" term. We will always install some loopback route, the question is whether we install it via ifa_maintain_loopback_route() or not.
Anyway, I've updated the description, hope it looks more clear now.