opensnoop: fix --cgroupmap with kfunc

Commit c347fe6 ("Support kfunc in opensnoop.py") introduces an
alternative probe on do_sys_open() with kfuncs instead of kprobes. This
new implementation is used if the kernel supports it. But it removed the
--cgroupmap filter added in commit b2aa29f ("tools: cgroup
filtering in execsnoop/opensnoop").

This patch adds the --cgroupmap filter in the kfunc implementation.

tools/opensnoop.py

@@ -177,6 +177,12 @@
  PID_TID_FILTER
  UID_FILTER
  FLAGS_FILTER
+#if CGROUPSET
+ u64 cgroupid = bpf_get_current_cgroup_id();
+ if (cgroupset.lookup(&cgroupid) == NULL) {
+ return 0;
+ }
+#endif
 
  struct data_t data = {};
  bpf_get_current_comm(&data.comm, sizeof(data.comm));