systemd: set Limit* to infinity

There is a not-insignificant performance overhead for all containers (if
containerd is a child of Docker, which is the current setup) if systemd
sets rlimits on the main Docker daemon process (because the limits
propogate to all children).

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

contrib/init/systemd/docker.service

@@ -17,6 +17,10 @@ Restart=always
 # /opt/containerd/bin is in front so dockerd grabs the correct runc binary
 Environment="PATH=/opt/containerd/bin:/sbin:/usr/bin:/usr/local/bin:$PATH"
 
+# Having non-zero Limit*s causes performance problems due to accounting overhead
+# in the kernel. We recommend using cgroups to do container-local accounting.
+LimitNOFILE=infinity
+LimitNPROC=infinity
 LimitCORE=infinity
 
 [Install]