Fix swapping of rack_id and nexus id params (#5578)

This let's add sled work again. I had broken it with a fix to another
bug in #5526.

nexus/src/app/mod.rs

@@ -378,8 +378,8 @@ impl Nexus {
             &background_ctx,
             Arc::clone(&db_datastore),
             &config.pkg.background_tasks,
+            rack_id,
             config.deployment.id,
-            config.deployment.rack_id,
             resolver.clone(),
             saga_request,
         );