nixos/systemd: fix TUN networking in LXC containers (#81481)

in LXC container /dev/net/tun is pre-available, "dev-net-tun.device" always fails

nixos/modules/system/boot/systemd.nix

@@ -73,7 +73,7 @@ let
       "systemd-journald.service"
       "systemd-journal-flush.service"
       "systemd-journal-catalog-update.service"
-      "systemd-journald-audit.socket"
+      ] ++ (optional (!config.boot.isContainer) "systemd-journald-audit.socket") ++ [
       "systemd-journald-dev-log.socket"
       "syslog.socket"
 
@@ -101,7 +101,7 @@ let
       "dev-hugepages.mount"
       "dev-mqueue.mount"
       "sys-fs-fuse-connections.mount"
-      "sys-kernel-config.mount"
+      ] ++ (optional (!config.boot.isContainer) "sys-kernel-config.mount") ++ [
       "sys-kernel-debug.mount"
 
       # Maintaining state across reboots.