The cgmanager socket has been moved to /sys/fs/cgroup/manager/sock.
The proxy moves that to /sys/fs/cgroup/manager.lower/sock then offers its own service over /sys/fs/cgroup/manager/sock. This allows a container to to have /sys/fs/cgroup/manager bind-mounted instead of the socket itself, allowing it to recover after the cgmanager on the host restarts.
The scm handling has been reworked. Now all *Scm dbus transactions complete as soon as the server receives the unix fd. It then reads the scm credentials (asynchronously) over the unix fd and sends the results to the client over the same fd.