Add PRODUCT_OTA_ENFORCE_VINTF_KERNEL_REQUIREMENTS to check_vintf_compatible_log

If kernel checks are missing, this can tell
us explicitly that the flag was disabled.

Test: pass
Change-Id: If5de88edbf352c163bc725c3e02a8cd29312e7f5
diff --git a/core/Makefile b/core/Makefile
index 95bac40..db8f11d 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -3934,7 +3934,8 @@
     $(if $(DEVICE_MANIFEST_SKUS),,EMPTY_VENDOR_SKU_PLACEHOLDER)) \
   $(DEVICE_MANIFEST_SKUS)
 $(check_vintf_compatible_log): $(HOST_OUT_EXECUTABLES)/checkvintf $(check_vintf_compatible_deps)
-	@echo -n -e 'Deps: \n  ' > $@
+	@echo "PRODUCT_OTA_ENFORCE_VINTF_KERNEL_REQUIREMENTS=$(PRODUCT_OTA_ENFORCE_VINTF_KERNEL_REQUIREMENTS)" > $@
+	@echo -n -e 'Deps: \n  ' >> $@
 	@sed 's/ /\n  /g' <<< "$(PRIVATE_CHECK_VINTF_DEPS)" >> $@
 	@echo -n -e 'Args: \n  ' >> $@
 	@cat <<< "$(PRIVATE_CHECK_VINTF_ARGS)" >> $@