Use -Werror in frameworks/native/cmds

* Remove unused variables.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: Ifde10b651abbdb2ab1e236ebe47e25bf6c4c9b23
diff --git a/cmds/ip-up-vpn/Android.mk b/cmds/ip-up-vpn/Android.mk
index 36bbdf5..e1e2204 100644
--- a/cmds/ip-up-vpn/Android.mk
+++ b/cmds/ip-up-vpn/Android.mk
@@ -18,6 +18,7 @@
 include $(CLEAR_VARS)
 
 LOCAL_SRC_FILES := ip-up-vpn.c
+LOCAL_CFLAGS := -Wall -Werror
 LOCAL_SHARED_LIBRARIES := libcutils liblog
 LOCAL_MODULE := ip-up-vpn
 LOCAL_MODULE_PATH := $(TARGET_OUT_ETC)/ppp