Flag-guard vfio_handler policies

vfio_handler will be active only if device assignment feature is turned
on.

Bug: 306563735
Test: microdroid tests with and without the flag
Change-Id: I5559dfca1a29852b65481c95f37edc9977ee9d7d
diff --git a/apex/com.android.virt-file_contexts b/apex/com.android.virt-file_contexts
index afe9f51..78720aa 100644
--- a/apex/com.android.virt-file_contexts
+++ b/apex/com.android.virt-file_contexts
@@ -3,4 +3,6 @@
 /bin/fd_server             u:object_r:fd_server_exec:s0
 /bin/virtmgr               u:object_r:virtualizationmanager_exec:s0
 /bin/virtualizationservice u:object_r:virtualizationservice_exec:s0
-/bin/vfio_handler          u:object_r:vfio_handler_exec:s0
+is_flag_enabled(RELEASE_AVF_ENABLE_DEVICE_ASSIGNMENT, `
+    /bin/vfio_handler          u:object_r:vfio_handler_exec:s0
+')