xrdp: do not restart xrdp-sesman on nixos-rebuild

nixos/modules/services/networking/xrdp.nix

···
         wantedBy = [ "multi-user.target" ];
         after = [ "network.target" ];
         description = "xrdp session manager";
+        restartIfChanged = false; # do not restart on "nixos-rebuild switch". like "display-manager", it can have many interactive programs as children
         serviceConfig = {
           ExecStart = "${cfg.package}/bin/xrdp-sesman --nodaemon --config ${confDir}/sesman.ini";
+          ExecStop  = "${pkgs.coreutils}/bin/kill -INT $MAINPID";
         };
       };