bpftool: Display cookie for tracing link probe

bpftool: Display cookie for tracing link probe

Display cookie for tracing link probe, in plain mode:

 #bpftool link
5: tracing  prog 34
	prog_type tracing  attach_type trace_fentry
	target_obj_id 1  target_btf_id 60355
	cookie 4503599627370496
	pids test_progs(176)

And in json mode:

 #bpftool link -j | jq
{
    "id": 5,
    "type": "tracing",
    "prog_id": 34,
    "prog_type": "tracing",
    "attach_type": "trace_fentry",
    "target_obj_id": 1,
    "target_btf_id": 60355,
    "cookie": 4503599627370496,
    "pids": [
      {
        "pid": 176,
        "comm": "test_progs"
      }
    ]
 }

Signed-off-by: Tao Chen <chen.dylane@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250606165818.3394397-3-chen.dylane@linux.dev