Add temporary filter to non-critical SNMP warning. (#13800)

A fix for this is available in the SNMP tip, but not in any Debian version.
This filter will be removed when Debian provides a version with the fix.

src/middlewared/middlewared/etc_files/syslog-ng/conf.d/tnfilters.conf.mako

@@ -60,6 +60,11 @@ filter f_scst {
   program("kernel") and match("dlm:" value("MESSAGE"));
 };
 
+# Temporary SNMP filter: NAS-129124
+filter f_snmp {
+  program("snmpd") and match("unexpected header length" value("MESSAGE"));
+};
+
 filter f_truenas_exclude {
 % if not nfs_conf['mountd_log']:
   not filter(f_nfs_mountd) and
@@ -69,7 +74,9 @@ filter f_truenas_exclude {
   not filter(f_containerd) and
   not filter(f_kube_router) and
   not filter(f_app_mounts) and
-  not filter(f_scst)
+  not filter(f_scst) and
+  # Temporary SNMP filter: NAS-129124
+  not filter(f_snmp)
 };
 
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