Where are you trying to ping X.X.X.228 from? If you're attempting to ping X.X.X.228 from any interface except br0, the NAT translation won't work since you have the inbound-interface set to br0.
You can try changing the inbound-interface to "+" which is a wildcard value (matches all interfaces). This will make the translation work regardless of where the request comes in.
set service nat rule 4000 inbound-interface +
