[sr-dev] [kamailio/kamailio] siptrace: aadded siptrace pseudo var (#2752)

[sergey-safarov]

#### Pre-Submission Checklist
- [x] Commit message has the format required by CONTRIBUTING guide
- [x] Commits are split per component (core, individual modules, libs, utils, ...)
- [ ] Each component has a single commit (if not, squash them into one commit)
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in `doc/` subfolder, the README file is autogenerated)

#### Type Of Change
- [ ] Small bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds new functionality)
- [ ] Breaking change (fix or feature that would change existing functionality)

#### Checklist:
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- [ ] PR should be backported to stable branches
- [ ] Tested changes locally
- [ ] Related to issue #XXXX (replace XXXX with an open issue number)

#### Description
I want to get the source (destination) IP address of the message during `event_route[siptrace:msg]` route.
I added the ability to get socket info in this route block.

Now added
```
$siptrace(src_uri)
$siptrace(dst_uri)
```
This pseudovars return string like
```
udp:8.8.8.8:5060
```

I think `src_uri` and `dst_uri` is not correct here because this socket info, not SIP uri.

I expecting suggestion on how to get these params and from current implementation:
```
src_ip
src_port
src_proto
dst_ip
dst_port
dst_proto
```

As reference, I take `sipdump` pseudovariable

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

https://github.com/kamailio/kamailio/pull/2752

-- Commit Summary --

* siptrace: aadded siptrace pseudo var

-- File Changes --

M src/modules/siptrace/siptrace.c (72)

-- Patch Links --

https://github.com/kamailio/kamailio/pull/2752.patch
https://github.com/kamailio/kamailio/pull/2752.diff

[Daniel-Constantin Mierla]

I hope to get the time to check if this is the best way during the next days. I expected it works with the usual variables, but maybe I am wrong and this new variable class is needed.