Stop prettifying JSON statistics

Passing the JSON_C_TO_STRING_PRETTY flag to
json_object_to_json_string_ext() makes the latter produce prettified
JSON output.  This results in a huge amount of redundant whitespace
being inserted into each HTTP response (whitespace amounts to about 40%
of the entire JSON payload).

The bandwidth cost can be amortized by enabling HTTP compression on the
client side ("Accept-Encoding: deflate"), but that does not affect the
size of data at rest.

Use the JSON_C_TO_STRING_PLAIN flag instead of JSON_C_TO_STRING_PRETTY
to minimize the size of JSON responses sent via the statistics channel.
External tools should be used for prettifying JSON data.

bin/named/statschannel.c

@@ -3332,7 +3332,7 @@ generatejson(named_server_t *server, size_t *msglen, const char **msg,
 	}
 
 	*msg = json_object_to_json_string_ext(bindstats,
-					      JSON_C_TO_STRING_PRETTY);
+					      JSON_C_TO_STRING_PLAIN);
 	*msglen = strlen(*msg);
 
 	if (rootp != NULL) {