nixos/docker: re-add network.target

Currently if docker starts concurrently with
firewall.service/systemd-networkd it breaks both due to iptables/netlink
logs.

nixos/modules/virtualisation/docker.nix

@@ -157,6 +157,7 @@ in
 
       systemd.services.docker = {
         wantedBy = optional cfg.enableOnBoot "multi-user.target";
+        after = [ "network.target" "docker.socket" ];
         requires = [ "docker.socket" ];
         environment = proxy_env;
         serviceConfig = {