[sr-dev] [kamailio/kamailio] tm: prevent t_suspend memory leak (#2763)

[Julien Chavanton]

When suspending while already in t_continue when processing a reply / suspending twice in a reply.

Thanks to @giavac  https://github.com/kamailio/kamailio/pull/2721 we can now suspend more then once in a reply route.

This is working well, however a memory leak was detected.

This modification is proposing a solution that will prevent calling `sip_msg_cloner` over an already twice over the same pointer, creating the memory leak.


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I assume this is a non "breaking change" since it can only trigger in a very the specific case that was not supported anyway.
Conditions when this alternate behavior can trigger:
1- must be in t_suspend
2- must be in a reply `if (msg->first_line.type == SIP_REPLY) {`
3- must have an already cloned `if (t->uac[branch].reply) {`

An alternate solution would be to free everything in the cloned message and recreate it.


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- [ ] Related to issue #XXXX (replace XXXX with an open issue number)

load test done that included connections, failures and timeouts while suspending multiple times.

```
 6(31) INFO: tm [t_suspend.c:126]: t_suspend(): [>>>SUSPEND<<<] cloning message !
53(78) INFO: tm [t_suspend.c:136]: t_suspend(): [>>>SUSPEND<<<] message already cloned, re-using ! 
```

```
Total 100000 INVITE calls sent in 1710825 ms at rate of 58/sec
Total 100000 connection responses received in 1714999 ms at rate of 58/sec:
>> Detailed connection responses received:
 - 200 connection responses:    24924     (OK)
 - 404 connection responses:    25145     (Not Found)
 - 408 connection responses:    24912     (Request Timeout)
 - 500 connection responses:    25019     (Internal Server Error)
>> Detailed disconnection responses received:
 - 200 disconnection responses:    24924     (OK)
                    ------
 TOTAL responses:    24924 (rate=14/sec)
```


#### Description
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You can view, comment on, or merge this pull request online at:

  https://github.com/kamailio/kamailio/pull/2763

-- Commit Summary --

  * tm: prevent t_suspend memory leak

-- File Changes --

    M src/modules/tm/t_suspend.c (21)

-- Patch Links --

https://github.com/kamailio/kamailio/pull/2763.patch
https://github.com/kamailio/kamailio/pull/2763.diff

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