BPF iterators[0] are a way to dump kernel data into user-space and an
alternative to `/proc` filesystem.
This change adds support for BPF iterators on the user-space side. It
provides a possibility to retrieve the outputs of BPF iterator programs
both from sync and async Rust code.
[0] https://docs.kernel.org/bpf/bpf_iterators.html
Michal Rostecki