bpftool: Fix bpftool net output

Print `bpftool net` output to stdout instead of stderr. Only errors
should be printed to stderr. Regular output should go to stdout and this
is what all other subcommands of bpftool do, including --json and
--pretty formats of `bpftool net` itself.

Fixes: commit f6f3bac08ff9 ("tools/bpf: bpftool: add net support")
Signed-off-by: Andrey Ignatov <[e-mail]>
Acked-by: Yonghong Song <[e-mail]>
Acked-by: Song Liu <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>

tools/bpf/bpftool/netlink_dumper.h

···
 		jsonw_name(json_wtr, name);		\
 		jsonw_start_object(json_wtr);		\
 	} else {					\
-		fprintf(stderr, "%s {", name);		\
+		fprintf(stdout, "%s {", name);		\
 	}						\
 }
 
···
 	if (json_output)				\
 		jsonw_start_object(json_wtr);		\
 	else						\
-		fprintf(stderr, "{");			\
+		fprintf(stdout, "{");			\
 }
 
 #define NET_END_OBJECT_NESTED				\
···
 	if (json_output)				\
 		jsonw_end_object(json_wtr);		\
 	else						\
-		fprintf(stderr, "}");			\
+		fprintf(stdout, "}");			\
 }
 
 #define NET_END_OBJECT					\
···
 	if (json_output)				\
 		jsonw_end_object(json_wtr);		\
 	else						\
-		fprintf(stderr, "\n");			\
+		fprintf(stdout, "\n");			\
 }
 
 #define NET_START_ARRAY(name, fmt_str)			\
···
 		jsonw_name(json_wtr, name);		\
 		jsonw_start_array(json_wtr);		\
 	} else {					\
-		fprintf(stderr, fmt_str, name);		\
+		fprintf(stdout, fmt_str, name);		\
 	}						\
 }
 
···
 	if (json_output)				\
 		jsonw_end_array(json_wtr);		\
 	else						\
-		fprintf(stderr, "%s", endstr);		\
+		fprintf(stdout, "%s", endstr);		\
 }
 
 #define NET_DUMP_UINT(name, fmt_str, val)		\
···
 	if (json_output)				\
 		jsonw_uint_field(json_wtr, name, val);	\
 	else						\
-		fprintf(stderr, fmt_str, val);		\
+		fprintf(stdout, fmt_str, val);		\
 }
 
 #define NET_DUMP_STR(name, fmt_str, str)		\
···
 	if (json_output)				\
 		jsonw_string_field(json_wtr, name, str);\
 	else						\
-		fprintf(stderr, fmt_str, str);		\
+		fprintf(stdout, fmt_str, str);		\
 }
 
 #define NET_DUMP_STR_ONLY(str)				\
···
 	if (json_output)				\
 		jsonw_string(json_wtr, str);		\
 	else						\
-		fprintf(stderr, "%s ", str);		\
+		fprintf(stdout, "%s ", str);		\
 }
 
 #endif