Add `BPF_PROG_TYPE_NETFILTER`

[ver-nyan]

The BPF_PROG_TYPE_NETFILTER program type was somewhat recently added v6.4+. Currently it shows up as Unknown when converting program type to string:

https://github.com/Netflix/bpftop/blob/c069b72210bafd1e85288372339e272d22136569/src/helpers.rs#L74

[ver-nyan]

oh, it looks like latest stable of libbpf-rs doesn't have the Netfilter variant yet.

https://github.com/libbpf/libbpf-rs/blob/8c7915809ec0c451d9acd517c875b85b545bd0c8/libbpf-rs/src/program.rs#L470

[jfernandez]

Also, one thing to consider for libbpf-rs updates: I'm also the Fedora package maintainer for bpftop, and each crate dependency also needs to be packaged for Fedora. So I try to keep the libbpf-rs version (and all other crate deps) in sync with the Fedora package version.