bugtool: Collect XFRM error counters twice

This commit changes the bugtool report to collect the XFRM error
counters (i.e., /proc/net/xfrm_stat) twice instead of only once. We will
collect at the beginning and end of the bugtool collection. In that way,
there will be around 5-6 seconds between the two collections and we may
see if any counter is currently increasing.

    $ diff cilium-bugtool-cilium-7d54p-20231025-115151/cmd/cat*--proc-net-xfrm_stat.md
    5c5
    < XfrmInStateProtoError   	4
    ---
    > XfrmInStateProtoError   	6

In this example, we can easily see that the XfrmInStateProtoError is
increasing. That suggests a key rotation issue is currently ongoing (cf.
IPsec troubleshooting docs).

I tried other approaches to collect over a longer timespan. That may
allow us to see slower increases. They all end up being more complex or
messier (we'd need to collect at beginning and end of the sysdump
instead). In the end, considering this is already a fallback plan for
when customers don't collect Prometheus metrics, I think the current,
simpler approach is good enough.

Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>

bugtool/cmd/configuration.go

@@ -81,6 +81,10 @@ func defaultCommands(confDir string, cmdDir string, k8sPods []string) []string {
 	var commands []string
 	// Not expecting all of the commands to be available
 	commands = []string{
+		// We want to collect this twice: at the very beginning and at the
+		// very end of the bugtool collection, to see if the counters are
+		// increasing.
+		"cat /proc/net/xfrm_stat",
 		// Host and misc
 		"ps auxfw",
 		"hostname",
@@ -214,6 +218,11 @@ func defaultCommands(confDir string, cmdDir string, k8sPods []string) []string {
 		commands = append(commands, tcCommands...)
 	}
 
+	// We want to collect this twice: at the very beginning and at the
+	// very end of the bugtool collection, to see if the counters are
+	// increasing.
+	commands = append(commands, "cat -u /proc/net/xfrm_stat")
+
 	return k8sCommands(commands, k8sPods)
 }
 
@@ -269,7 +278,6 @@ func tcInterfaceCommands() ([]string, error) {
 
 func catCommands() []string {
 	files := []string{
-		"/proc/net/xfrm_stat",
 		"/proc/sys/net/core/bpf_jit_enable",
 		"/proc/kallsyms",
 		"/etc/resolv.conf",