[PATCH bpf-next 1/2] bpftool: fix printing of pointer value

[Manu Bretelle <chantr4@xxxxxxxxx>]

When printing a pointer value, "%p" will either print the hexadecimal
value of the pointer (e.g `0x1234`), or `(nil)` when NULL.

Both of those are invalid json "integer" values and need to be wrapped
in quotes.

Before:
```
$ sudo bpftool struct_ops dump  name ned_dummy_cca | grep next
                    "next": (nil),
$ sudo bpftool struct_ops dump  name ned_dummy_cca | \
    jq '.[1].bpf_struct_ops_tcp_congestion_ops.data.list.next'
parse error: Invalid numeric literal at line 29, column 34
```

After:
```
$ sudo ./bpftool struct_ops dump  name ned_dummy_cca | grep next
                    "next": "(nil)",
$ sudo ./bpftool struct_ops dump  name ned_dummy_cca | \
    jq '.[1].bpf_struct_ops_tcp_congestion_ops.data.list.next'
"(nil)"
```

Signed-off-by: Manu Bretelle <chantr4@xxxxxxxxx>
---
 tools/bpf/bpftool/btf_dumper.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/bpf/bpftool/btf_dumper.c b/tools/bpf/bpftool/btf_dumper.c
index 1b7f69714604..527fe867a8fb 100644
--- a/tools/bpf/bpftool/btf_dumper.c
+++ b/tools/bpf/bpftool/btf_dumper.c
@@ -127,7 +127,7 @@ static void btf_dumper_ptr(const struct btf_dumper *d,
 
 print_ptr_value:
 	if (d->is_plain_text)
-		jsonw_printf(d->jw, "%p", (void *)value);
+		jsonw_printf(d->jw, "\"%p\"", (void *)value);
 	else
 		jsonw_printf(d->jw, "%lu", value);
 }
-- 
2.39.3