Restore `Type=notify` in Systemd unit

Signed-off-by: Valentin Kulesh <valentin.kulesh@virtuozzo.com>

contrib/init/systemd/docker.service

@@ -6,6 +6,7 @@ After=network-online.target firewalld.service
 Wants=network-online.target
 
 [Service]
+Type=notify
 # the default is not to use systemd for cgroups because the delegate issues still
 # exists and systemd currently does not support the cgroup feature set required
 # for containers run by docker