add alerts for node softnet

Add alerts NodeSoftNetTimesSqueezed and NodeSoftNetBacklogLength

Partially revert "fix: tune net.core.netdev_budget"
This partially reverts commit 6b7accacd089c740ae2ba92405d32e0e9f64b4dc.
And re-introduce alert NodeSoftNetTimesSqueezed

Add new alert NodeSoftNetBacklogLength
diff --git a/roles/kube_prometheus_stack/files/jsonnet/legacy.libsonnet b/roles/kube_prometheus_stack/files/jsonnet/legacy.libsonnet
index 3489639..3300e66 100644
--- a/roles/kube_prometheus_stack/files/jsonnet/legacy.libsonnet
+++ b/roles/kube_prometheus_stack/files/jsonnet/legacy.libsonnet
@@ -172,6 +172,14 @@
         name: 'softnet',
         rules: [
           {
+            alert: 'NodeSoftNetBacklogLength',
+            expr: 'sum(node_softnet_backlog_len) by (instance) > 5000',
+            'for': '1m',
+            labels: {
+              severity: 'critical',
+            },
+          },
+          {
             alert: 'NodeSoftNetDrops',
             expr: 'sum(rate(node_softnet_dropped_total[1m])) by (instance) != 0',
             'for': '1m',
@@ -179,6 +187,14 @@
               severity: 'critical',
             },
           },
+          {
+            alert: 'NodeSoftNetTimesSqueezed',
+            expr: 'sum(rate(node_softnet_times_squeezed_total[1m])) by (instance) > 10',
+            'for': '10m',
+            labels: {
+              severity: 'warning',
+            },
+          },
         ],
       },
     ],