tools/bpftool: Emit name <anon> for anonymous BTFs

For consistency of output, emit "name <anon>" for BTFs without the name. This
keeps output more consistent and obvious.
Suggested-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201202065244.530571-2-andrii@kernel.org

tools/bpf/bpftool/btf.c

@@ -750,6 +750,8 @@ show_btf_plain(struct bpf_btf_info *info, int fd,
 		printf("name [%s]  ", name);
 	else if (name && name[0])
 		printf("name %s  ", name);
+	else
+		printf("name <anon>  ");
 	printf("size %uB", info->btf_size);
 
 	n = 0;