Label /vendor_file_contexts as file_contexts_file

vendor_init doesn't have permissions to read rootfs labeled files, but
needs to read /vendor_file_contexts to do restorecon correctly.  This
file is a file_contexts file, so labeling it as such seems appropriate.

Test: bullhead + vendor_init doesn't hit this audit
Change-Id: I475e9735616c2426b9c7073700272f878ced2135
diff --git a/init/selinux.cpp b/init/selinux.cpp
index 1febccd..d3ce236 100644
--- a/init/selinux.cpp
+++ b/init/selinux.cpp
@@ -420,6 +420,7 @@
 
     selinux_android_restorecon("/plat_file_contexts", 0);
     selinux_android_restorecon("/nonplat_file_contexts", 0);
+    selinux_android_restorecon("/vendor_file_contexts", 0);
     selinux_android_restorecon("/plat_property_contexts", 0);
     selinux_android_restorecon("/nonplat_property_contexts", 0);
     selinux_android_restorecon("/plat_seapp_contexts", 0);