Support defaults properties in java_system_module

Test: none
Change-Id: I08e5c39690b3c9960dc5e99c4b866a2523c9eafb
diff --git a/java/system_modules.go b/java/system_modules.go
index 9ee0307..8005360 100644
--- a/java/system_modules.go
+++ b/java/system_modules.go
@@ -87,11 +87,13 @@
 	module := &SystemModules{}
 	module.AddProperties(&module.properties)
 	android.InitAndroidArchModule(module, android.HostAndDeviceSupported, android.MultilibCommon)
+	android.InitDefaultableModule(module)
 	return module
 }
 
 type SystemModules struct {
 	android.ModuleBase
+	android.DefaultableModuleBase
 
 	properties SystemModulesProperties