rules: fixed leak/panic when parsing/loading lists

Rules of type lists [domains, IPs, network ranges] are reloaded
whenever a file containing the data changes.

One could expect to update these files once or twice a day, but
by updating the files continuously it was possible to cause a leak,
leading to a crash.

daemon/rule/operator.go

@@ -233,6 +233,9 @@ func (o *Operator) reListCmp(v interface{}) bool {
 	if o.Sensitive == false {
 		dstHost = strings.ToLower(dstHost)
 	}
+	o.RLock()
+	defer o.RUnlock()
+
 	for file, re := range o.lists {
 		r := re.(*regexp.Regexp)
 		if r.MatchString(dstHost) {