xsession: fix multiple arguments with logToJournal

KDM and LightDM (at least with autologin) call the xsession-script with
two arguments: the first is the path of the xsession script itself,
while the second one are the actual arguments. The line to re-exec the
script under systemd-cat only forwarded a single argument, therefore
breaking LightDM and KDM login. This commit fixes the issue by always
forwarding all the arguments.

nixos/modules/services/x11/display-managers/default.nix

@@ -34,7 +34,7 @@ let
 
       ${optionalString cfg.displayManager.logToJournal ''
         if [ -z "$_DID_SYSTEMD_CAT" ]; then
-          _DID_SYSTEMD_CAT=1 exec ${config.systemd.package}/bin/systemd-cat -t xsession -- "$0" "$1"
+          _DID_SYSTEMD_CAT=1 exec ${config.systemd.package}/bin/systemd-cat -t xsession -- "$0" "$@"
         fi
       ''}