librenms: Replace deprecated OID 'ssCpuIdle' with 'ssCpuRawIdle'

The 'ssCpuIdle' OID has been deprecated in favor of 'ssCpuRawIdle', which
provides more accurate CPU usage metrics over any desired time period.

This commit updates the OID used in LibreNMS from 'ssCpuIdle' to 'ssCpuRawIdle'
in FsSwitch.php to ensure more reliable CPU usage monitoring.

Changes:
- Replaced 'ssCpuIdle' with 'ssCpuRawIdle' in the SNMP walk.
- Updated the CPU usage calculation to use 'ssCpuRawIdle'.

Bug: T285229
Change-Id: I63120ccc03b597d5b9623a77a0f9e6ebd7b6cf3e

LibreNMS/OS/FsSwitch.php

@@ -41,18 +41,29 @@ public function discoverProcessors()
     {
         $processors = [];
 
+        // Get the number of CPUs
+        $num_cpus_data = snmpwalk_cache_oid($this->getDeviceArray(), 'ssCpuNumCpus', [], 'UCD-SNMP-MIB');
+        $num_cpus = isset($num_cpus_data[0]['ssCpuNumCpus']) ? $num_cpus_data[0]['ssCpuNumCpus'] : 1;
+
+         // Assuming a tick rate of 100 ticks per second
+        $ticks_per_second = 100;
+
         // Tests OID from SWITCH MIB.
-        $processors_data = snmpwalk_cache_oid($this->getDeviceArray(), 'ssCpuIdle', [], 'SWITCH', 'fs');
+        $processors_data = snmpwalk_cache_oid($this->getDeviceArray(), 'ssCpuRawIdle', [], 'SWITCH', 'fs');
 
         foreach ($processors_data as $index => $entry) {
+            // Calculate total ticks for all CPUs
+            $total_ticks = $num_cpus * $ticks_per_second;
+            $idle_percentage = ($entry['ssCpuRawIdle'] / $total_ticks) * 100;
+
             $processors[] = Processor::discover(
                 'fs-SWITCHMIB',
                 $this->getDeviceId(),
                 '.1.3.6.1.4.1.27975.1.2.11.' . $index,
                 $index,
                 'CPU',
                 -1,
-                100 - $entry['ssCpuIdle']
+                100 - $idle_percentage
             );
         }