Ignore already existing cgroupv2 mount point (#427)

When the process in an container gets restarted, they reuse the same
filesystem. This means that the mount point we need for mounting
cgroupv2 already exists and we should not fail.

pkg/ebpftracer/module_linux.go

@@ -10,10 +10,7 @@ import (
 
 func mountCgroup2(mountPoint string) error {
 	err := os.Mkdir(mountPoint, 0755)
-	if err != nil {
-		if os.IsExist(err) {
-			return nil
-		}
+	if err != nil && !os.IsExist(err){
 		return fmt.Errorf("creating directory at %q: %w", mountPoint, err)
 	}
 	// https://docs.kernel.org/admin-guide/cgroup-v2.html#mounting