sepolicy: fix missing label on vendor_service_contexts

Vendors can publish services with servicemanager only on non-Treble
builds. vendor_service_contexts is not meant to be read by
servicemanager.

https://android.googlesource.com/platform/system/sepolicy/+/5bccbfefe494aa6fed73a58d80713e28257ba7f1/public/servicemanager.te#22

Bug: 141333155
Test: create /vendor/etc/selinux/vendor_service_contexts and make sure it is
correctly labeled.
Change-Id: Ib68c50e0cdb2c39f0857a10289bfa26fa11b1b3c
2 files changed