bpftool: Extend net dump with netkit progs

Add support to dump BPF programs on netkit via bpftool. This includes both
the BPF link and attach ops programs. Dumped information contain the attach
location, function entry name, program ID and link ID when applicable.

Example with tc BPF link:

  # ./bpftool net
  xdp:

  tc:
  nk1(22) netkit/peer tc1 prog_id 43 link_id 12

  [...]

Example with json dump:

  # ./bpftool net --json | jq
  [
    {
      "xdp": [],
      "tc": [
        {
          "devname": "nk1",
          "ifindex": 18,
          "kind": "netkit/primary",
          "name": "tc1",
          "prog_id": 29,
          "prog_flags": [],
          "link_id": 8,
          "link_flags": []
        }
      ],
      "flow_dissector": [],
      "netfilter": []
    }
  ]

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20231024214904.29825-6-daniel@iogearbox.net
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>