ModSecurity blocks requests

When enabling mod_security there is strange problem with connection. After enabling it, few minutes latter all connections timing out.

It is easy to reproduce:

1. Install nginx with modsec enabled;
2. Load modsec:

```
modsecurity on;
modsecurity_rules_file /etc/nginx/modsec/main.conf;
```
3. Visit your website, few pages. Eventually you will encounter infinite loading and timeout.

Maybe related, error.log contains:

```
2021/02/13 10:17:53 [alert] 31891#31891: *330 open socket #37 left in connection 8
2021/02/13 10:17:53 [alert] 31891#31891: *329 open socket #35 left in connection 9
2021/02/13 10:17:53 [alert] 31891#31891: aborting
```