agent: Ensure proper cgroupsV2 with init_mode=yes

When the agent is run as the init process cgroupfs is being
setup. In the case of cgroupsV1 we needed to enable the memory hiearchy
this is now per default enabled in cgroupsV2. Additionally the file
/sys/fs/cgroup/memory/memory.use_hierarchy isn't even available with V2.

Signed-off-by: Zvonko Kaiser <zkaiser@nvidia.com>

src/agent/src/mount.rs

@@ -299,7 +299,13 @@ pub fn cgroups_mount(logger: &Logger, unified_cgroup_hierarchy: bool) -> Result<
 
     // Enable memory hierarchical account.
     // For more information see https://www.kernel.org/doc/Documentation/cgroup-v1/memory.txt
-    online_device("/sys/fs/cgroup/memory/memory.use_hierarchy")
+    // cgroupsV2 will automatically enable memory.use_hierarchy.
+    // additinoally this directory layout is not present in cgroupsV2.
+    if !unified_cgroup_hierarchy {
+        return online_device("/sys/fs/cgroup/memory/memory.use_hierarchy");
+    }
+
+    Ok(())
 }
 
 #[instrument]