Merge pull request #8451 from eparis/systemd

Fix system socket/service unit files

contrib/init/systemd/docker.service

@@ -10,4 +10,4 @@ LimitNOFILE=1048576
 LimitNPROC=1048576
 
 [Install]
-Also=docker.socket
+WantedBy=multi-user.target

contrib/init/systemd/docker.socket

@@ -1,5 +1,6 @@
 [Unit]
 Description=Docker Socket for the API
+PartOf=docker.service
 
 [Socket]
 ListenStream=/var/run/docker.sock