Call the rest of the middleware stack all the time.

plugins/providers/virtualbox/action/destroy_unused_network_interfaces.rb

@@ -13,8 +13,8 @@ module VagrantPlugins
           if env[:machine].provider_config.destroy_unused_network_interfaces
             @logger.info("Destroying unused network interfaces...")
             env[:machine].provider.driver.delete_unused_host_only_networks
-            @app.call(env)
           end
+          @app.call(env)
         end
       end
     end