netcfg: turn on -Werror

- resolve unused variable reference

Change-Id: If725a1cb0ee645c6e379c9ce21ab8c40bc4cd554
diff --git a/netcfg/Android.mk b/netcfg/Android.mk
index 949f417..fc01a54 100644
--- a/netcfg/Android.mk
+++ b/netcfg/Android.mk
@@ -11,6 +11,7 @@
 #LOCAL_STATIC_LIBRARIES := libcutils libc
 
 LOCAL_SHARED_LIBRARIES := libc libnetutils
+LOCAL_CFLAGS := -Werror
 
 include $(BUILD_EXECUTABLE)
 endif