systemd: don't limit tasks

Systemd sets a default of 512 tasks, which is far
too low to run many containers.

Note that TasksMax is only supported on systemd 226
and above.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

contrib/init/systemd/docker.service

@@ -23,5 +23,9 @@ LimitNOFILE=infinity
 LimitNPROC=infinity
 LimitCORE=infinity
 
+# Comment TasksMax if your systemd version does not supports it.
+# Only systemd 226 and above support this option.
+TasksMax=infinity
+
 [Install]
 WantedBy=multi-user.target