Fix race condition in WebSocketService. (#1021)

Signed-off-by: Adrian Sutton <adrian.sutton@consensys.net>

ethereum/jsonrpc/src/main/java/tech/pegasys/pantheon/ethereum/jsonrpc/websocket/WebSocketService.java

@@ -181,7 +181,7 @@ public class WebSocketService {
         LOG.info(
             "Websocket service started and listening on {}:{}",
             configuration.getHost(),
-            httpServer.actualPort());
+            res.result().actualPort());
 
         resultFuture.complete(null);
       } else {