Default uninstallable modules' tag to optional

Change-Id: I31faee42c807b3b6d7b85feea6c74860c89d45de
diff --git a/core/base_rules.mk b/core/base_rules.mk
index 5bb6b77..3c11673 100644
--- a/core/base_rules.mk
+++ b/core/base_rules.mk
@@ -57,8 +57,12 @@
 
 LOCAL_MODULE_TAGS := $(sort $(LOCAL_MODULE_TAGS))
 ifeq (,$(LOCAL_MODULE_TAGS))
-# Modules without tags fall back to user (which is changed to user eng below)
+ifeq (true,$(LOCAL_UNINSTALLABLE_MODULE))
+LOCAL_MODULE_TAGS := optional
+else
+# Installable modules without tags fall back to user (which is changed to user eng below)
 LOCAL_MODULE_TAGS := user
+endif
 #$(warning default tags: $(lastword $(filter-out config/% out/%,$(MAKEFILE_LIST))))
 endif