tools/bpftool: show btf_id in map listing

Let's print btf id of map similar to the way we are printing it
for programs.

Sample output:
user@test# bpftool map -f
61: lpm_trie  flags 0x1
	key 20B  value 8B  max_entries 1  memlock 4096B
133: array  name test_btf_id  flags 0x0
	key 4B  value 4B  max_entries 4  memlock 4096B
	pinned /sys/fs/bpf/test100
	btf_id 174
170: array  name test_btf_id  flags 0x0
	key 4B  value 4B  max_entries 4  memlock 4096B
	btf_id 240
Signed-off-by: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/map.c

@@ -531,6 +531,9 @@ static int show_map_close_json(int fd, struct bpf_map_info *info)
 	}
 	close(fd);
 
+	if (info->btf_id)
+		jsonw_int_field(json_wtr, "btf_id", info->btf_id);
+
 	if (!hash_empty(map_table.table)) {
 		struct pinned_obj *obj;
 
@@ -606,6 +609,9 @@ static int show_map_close_plain(int fd, struct bpf_map_info *info)
 		}
 	}
 
+	if (info->btf_id)
+		printf("\n\tbtf_id %d", info->btf_id);
+
 	printf("\n");
 	return 0;
 }