Try to use aya only in userspce (as the 1st step)

Rewriting lockc fully in Rust with Aya is a heavy task and we had a hard time doing it at once.

It should be possible to use Aya only in userspace and load eBPF programs written in C with it. That should make the transition easier, potentially allowing us to rewrite eBPF programs in chunks (programs sharing the same maps will have to be rewritten together).