Revert "libct: Don't use stale fds"

Want to verify the CI breaks now.

libcontainer/rootfs_linux.go

@@ -60,16 +60,15 @@ func prepareRootfs(pipe io.ReadWriter, iConfig *initConfig, mountFds []int) (err
 		return fmt.Errorf("malformed mountFds slice. Expected size: %v, got: %v. Slice: %v", len(config.Mounts), len(mountFds), mountFds)
 	}
 
+	mountConfig := &mountConfig{
+		root:            config.Rootfs,
+		label:           config.MountLabel,
+		cgroup2Path:     iConfig.Cgroup2Path,
+		rootlessCgroups: iConfig.RootlessCgroups,
+		cgroupns:        config.Namespaces.Contains(configs.NEWCGROUP),
+	}
 	setupDev := needsSetupDev(config)
 	for i, m := range config.Mounts {
-		mountConfig := &mountConfig{
-			root:            config.Rootfs,
-			label:           config.MountLabel,
-			cgroup2Path:     iConfig.Cgroup2Path,
-			rootlessCgroups: iConfig.RootlessCgroups,
-			cgroupns:        config.Namespaces.Contains(configs.NEWCGROUP),
-		}
-
 		// Just before the loop we checked that if not empty, len(mountFds) == len(config.Mounts).
 		// Therefore, we can access mountFds[i] without any concerns.
 		if mountFds != nil && mountFds[i] != -1 {