Show tid or pid of iterators if giving an argument of tid or pid

For example, the command `bpftool link list` may list following
lines.

1: iter  prog 2  target_name bpf_map
2: iter  prog 3  target_name bpf_prog
33: iter  prog 225  target_name task_file  tid 1644
        pids test_progs(1644)

Link 33 is a task_file iterator with tid 1644.  For now, only targets
of task, task_file and task_vma may be with tid or pid to filter out
tasks other than those belonging to a process (pid) or a thread (tid).
Signed-off-by: Kui-Feng Lee <kuifeng@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Quentin Monnet <quentin@isovalent.com>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/bpf/20220926184957.208194-6-kuifeng@fb.com