Make vendor_init check SELinux before setting properties

Finishing a TODO from vendor_init, check SELinux permissions before
setting properties in vendor_init.

Bug: 62875318
Test: N/A
Change-Id: I3cb6abadd2613ae083705cc6b9c970587b6c6b19
diff --git a/init/subcontext.proto b/init/subcontext.proto
index e68115e..c31f4fb 100644
--- a/init/subcontext.proto
+++ b/init/subcontext.proto
@@ -38,4 +38,10 @@
         Failure failure = 2;
         ExpandArgsReply expand_args_reply = 3;
     }
+
+    message PropertyToSet {
+        optional string name = 1;
+        optional string value = 2;
+    }
+    repeated PropertyToSet properties_to_set = 4;
 }
\ No newline at end of file