Limit concurrent connections from a single IP address

>Draft CIS Benchmark 1.1.8

## Description
It might be worthwhile mentioning the following configuration parameters: limit\_conn limit\_conn\_zone (sets shared memory zone) They are used to limit the number of connections per IP address. https://nginx.org/en/docs/stream/ngx\_stream\_limit\_conn\_module.html

## Rationale
The traffic normally originates from a fixed set of IP addresses, belonging to the machines used to carry out the attack. As a result, each IP address is responsible for many more connections and requests than you would expect from a real user.

## Remediation
None provided

## Audit
None provided