bpftool: Show also the name of type BPF_OBJ_LINK

For example, /sys/fs/bpf/maps.debug is a BPF link. When you run `bpftool map show`
to show it:

Before:

  $ bpftool map show pinned /sys/fs/bpf/maps.debug
  Error: incorrect object type: unknown

After:

  $ bpftool map show pinned /sys/fs/bpf/maps.debug
  Error: incorrect object type: link

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20220629154832.56986-5-laoar.shao@gmail.com