I would report it as spam (or link spam) since link dumps are also spam after all. However, interestingly, spam is also not clearly mentioned   (because imho spam can be different from 0-value and from off topic). But I have reported a spam many times and it was ok.

So yes, I agree, a clear rule about link dumps would be welcome (and I would add a clear separate rule on spam too).


But, as a "closing word", I think that one can report as anything close enough to what's the problem there, really. The mods can handle that very good even if it's not 100% by the book.