Better linked-list traversal in BPF

There's hash tables that do this. But I think in reality that's kind of just otherthinking it. Very few C programs use linked lists for good reasons and want or need any of the very few positive properties of them. It's mostly just used because it's the first thing you learn in school and perhaps more importantly the only datastructure that's easy to implement and use in C without macro hell. That and not nearly enough people tell programmers it's a bad idea.*

* this goes beyond just performance implications but architectural decisions too. One of the "advantages" of linked lists is that list items rarely move once they get created. This inevitably leads to things like structures getting bloated with information really only needed by one user and people stashing long-lived pointers to objects on lists somewhere without really worrying about how long they'll stay valid for, which ossifies into the familiar pointer hell codebase where you're scared of changing anything because something might still be holding a pointer to it and 5% of your CPU time is refcounting. But I digress.