Merge pull request #15119 from xnox/sdnotify

systemd: set service type to notify.

contrib/init/systemd/docker.service

@@ -5,6 +5,7 @@ After=network.target docker.socket
 Requires=docker.socket
 
 [Service]
+Type=notify
 ExecStart=/usr/bin/docker daemon -H fd://
 MountFlags=slave
 LimitNOFILE=1048576