nixos, openafs-client: correct serviceConfig

Changed files
+1
nixos
modules
services
network-filesystems
openafs-client
+1
nixos/modules/services/network-filesystems/openafs-client/default.nix
···
description = "AFS client";
wantedBy = [ "multi-user.target" ];
after = [ "network.target" ];
+
serviceConfig = { RemainAfterExit = true; };
preStart = ''
mkdir -p -m 0755 /afs