Add SELinux policy for using userfaultfd

ART runtime will be using userfaultfd for a new heap compaction
algorithm. After enabling userfaultfd in android kernels (with SELinux
support), the feature needs policy that allows { create ioctl read }
operations on userfaultfd file descriptors.

Bug: 160737021
Test: Manually tested by exercising userfaultfd ops in ART
Change-Id: I9ccb7fa9c25f91915639302715f6197d42ef988e
diff --git a/private/access_vectors b/private/access_vectors
index a02a2a8..7e5e7a5 100644
--- a/private/access_vectors
+++ b/private/access_vectors
@@ -182,6 +182,9 @@
 	entrypoint
 }
 
+class anon_inode
+inherits file
+
 class lnk_file
 inherits file