### Description

On systems with a high number of TCP sessions there can be a significant performance regression observed, probably related to the newly added TCP connection tracking feature.

### Troubleshooting

#### Reproduction

No special configuration is necessary, just install the latest 5.7.x release, e.g. 5.7.3 on a production system with a lot of clients connected over TCP or TLS. You need to have a large number of clients connected to be able to observe the regression. For a high number of connections (e.g. more then 20.000 up to 30.000 connections) the Kamailio servers uses about 30% to 50% more CPU as with the old version.

#### Debugging Data

Two graphs were attached to this issue. The first shows the CPU load before (less load) and after the upgrade (increased load). The second is a flamegraph that shows that over 80% of the CPU time is spent in the newly added function tcp_connection_limit_srcip().

<img width="372" alt="cpu-load-before-after" src="https://github.com/kamailio/kamailio/assets/6481937/ec92c41b-25e2-4847-a4bc-b344ccb3ebe3"> 

Most of the CPU time is spend in the TCP main process, as expected.

#### Log Messages

No special log messages could be observed.

#### SIP Traffic

### Possible Solutions

The TCP limit feature should probably be optimized to not cause such a large performance regression. It should be also possible to deactivate it completly and therefore getting a comparable performance as before the feature addition.

### Additional Information

Kamailio 5.7.3 and probably also git master version.

* **Operating System**:

Debian 11, Debian 12