fix: change kprobe for cpu usage (#233)

Change the kprobe for CPU usage to probe the cpu accounting
function instead of the cgroup accounting function. This addresses
an issue where all CPU time is reported as idle on some systems.

src/samplers/cpu/linux/usage/mod.bpf.c

@@ -44,8 +44,8 @@ int account_delta(u64 delta, u32 usage_idx)
 	return 0;
 }
 
-SEC("kprobe/__cgroup_account_cputime_field")
-int BPF_KPROBE(cgroup_account_cputime_field_kprobe, void *task, u32 index, u64 delta)
+SEC("kprobe/cpuacct_account_field")
+int BPF_KPROBE(cpuacct_account_field_kprobe, void *task, u32 index, u64 delta)
 {
 	if (index == 3) {
 		return 0;