Add MAINLINE_SEPOLICY_DEV_CERTIFICATES to keys.conf

DEFAULT_SYSTEM_DEV_CERTIFICATE is not appropriate as some OEMs may need
to change only the certificates used to generate
plat_mac_permissions.xml for mainline modules.

Test: m, checked output plat_mac_permissions.xml
Bug: 138097611
Bug: 134995443
Change-Id: Ie19130a243db043f432039c54c379f06e60ab6c6
diff --git a/mac_permissions.mk b/mac_permissions.mk
index 7cb1b98..3a28197 100644
--- a/mac_permissions.mk
+++ b/mac_permissions.mk
@@ -27,6 +27,7 @@
 $(all_plat_mac_perms_files) $(all_plat_keys)
 	@mkdir -p $(dir $@)
 	$(hide) DEFAULT_SYSTEM_DEV_CERTIFICATE="$(dir $(DEFAULT_SYSTEM_DEV_CERTIFICATE))" \
+		MAINLINE_SEPOLICY_DEV_CERTIFICATES="$(MAINLINE_SEPOLICY_DEV_CERTIFICATES)" \
 		$(HOST_OUT_EXECUTABLES)/insertkeys.py -t $(TARGET_BUILD_VARIANT) -c $(TOP) $< -o $@ $(PRIVATE_MAC_PERMS_FILES)
 
 all_plat_keys :=
diff --git a/private/keys.conf b/private/keys.conf
index f517b67..362e73d 100644
--- a/private/keys.conf
+++ b/private/keys.conf
@@ -15,7 +15,7 @@
 ALL : $DEFAULT_SYSTEM_DEV_CERTIFICATE/media.x509.pem
 
 [@NETWORK_STACK]
-ALL : $DEFAULT_SYSTEM_DEV_CERTIFICATE/networkstack.x509.pem
+ALL : $MAINLINE_SEPOLICY_DEV_CERTIFICATES/networkstack.x509.pem
 
 [@SHARED]
 ALL : $DEFAULT_SYSTEM_DEV_CERTIFICATE/shared.x509.pem