buildroot upgrade

jkt: Also, refactor that custom Unix group handling in buildroot to make
it unconditional. Fewer options, less work.

jkt: Also rebase systemd patch (now at lldp-json-250.4)

Change-Id: Icd8c22b8a2e6e9d0e3346a103bcfbcd78aecabac
Co-authored-by: Jan Kundrát <jan.kundrat@cesnet.cz>
diff --git a/board/czechlight/common/patches/systemd/0004-varlink-Implement-varlink_observe_complete.patch b/board/czechlight/common/patches/systemd/0004-varlink-Implement-varlink_observe_complete.patch
index ca5c9f0..a181c0e 100644
--- a/board/czechlight/common/patches/systemd/0004-varlink-Implement-varlink_observe_complete.patch
+++ b/board/czechlight/common/patches/systemd/0004-varlink-Implement-varlink_observe_complete.patch
@@ -1,4 +1,4 @@
-From 4e7bdd09a12d9ed1695980d8edf94841a5c11cd8 Mon Sep 17 00:00:00 2001
+From 072ebba1de115cb31a71f6398c17a1bfdb383ee8 Mon Sep 17 00:00:00 2001
 From: Tomas Pecka <peckato1@users.noreply.github.com>
 Date: Thu, 9 Sep 2021 09:19:05 +0200
 Subject: [PATCH 4/9] varlink: Implement varlink_observe_complete
@@ -70,5 +70,5 @@
  /* Enqueue a final reply */
  int varlink_reply(Varlink *v, JsonVariant *parameters);
 -- 
-2.34.1
+2.35.1