udevadm: automatically anable JSON-SEQ in case JSON is used for "udevadm info -a"

We are going to output a series of JSON objects, hence let's
automatically enable JSON-SEQ output mode, as we usually do.

"jq --seq" supports this natively, hence this should not really restrict
us.

Follow-up for: 67ea8a4c0e

src/udev/udevadm-info.c

@@ -274,6 +274,8 @@ static int print_device_chain_in_json(sd_device *device) {
 
         assert(device);
 
+        arg_json_format_flags |=SD_JSON_FORMAT_SEQ;
+
         r = print_all_attributes_in_json(device, /* is_parent = */ false);
         if (r < 0)
                 return r;