common: Copy APN list to $(TARGET_COPY_OUT_PRODUCT)/etc

This handles GSI product

Change-Id: I5754ff9c020e094c5ca5bd08e0572584009558ee
diff --git a/prebuilt/common/Android.mk b/prebuilt/common/Android.mk
index 83eecee..8798974 100644
--- a/prebuilt/common/Android.mk
+++ b/prebuilt/common/Android.mk
@@ -10,7 +10,7 @@
 include $(BUILD_PREBUILT)
 
 ################################
-# Copies the APN list file into system/etc for the product as apns-conf.xml.
+# Copies the APN list file into $(TARGET_COPY_OUT_PRODUCT)/etc for the product as apns-conf.xml.
 # In the case where $(CUSTOM_APNS_FILE) is defined, the content of $(CUSTOM_APNS_FILE)
 # is added or replaced to the $(DEFAULT_APNS_FILE).
 include $(CLEAR_VARS)
@@ -35,4 +35,6 @@
 
 LOCAL_PREBUILT_MODULE_FILE := $(FINAL_APNS_FILE)
 
+LOCAL_PRODUCT_MODULE := true
+
 include $(BUILD_PREBUILT)