- Mention when FR timeout is reached, and which of FR timers expired - Log when starting FR/RETR timers - log when changing default timeouts to user-set values - log when resetting fr/retr timers on provisional replies

<!-- Kamailio Pull Request Template -->

<!-- IMPORTANT: - for detailed contributing guidelines, read: https://github.com/kamailio/kamailio/blob/master/.github/CONTRIBUTING.md - pull requests must be done to master branch, unless they are backports of fixes from master branch to a stable branch - backports to stable branches must be done with 'git cherry-pick -x ...' - code is contributed under BSD for core and main components (tm, sl, auth, tls) - code is contributed GPLv2 or a compatible license for the other components - GPL code is contributed with OpenSSL licensing exception -->

#### Pre-Submission Checklist <!-- Go over all points below, and after creating the PR, tick all the checkboxes that apply --> <!-- All points should be verified, otherwise, read the CONTRIBUTING guidelines from above--> <!-- If you're unsure about any of these, don't hesitate to ask on sr-dev mailing list --> - [X] Commit message has the format required by CONTRIBUTING guide - [X] Commits are split per component (core, individual modules, libs, utils, ...) - [X] Each component has a single commit (if not, squash them into one commit) - [X] No commits to README files for modules (changes must be done to docbook files in `doc/` subfolder, the README file is autogenerated)

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

#### Checklist: <!-- Go over all points below, and after creating the PR, tick the checkboxes that apply --> - [X] PR should be backported to stable branches - [ ] Tested changes locally - [ ] Related to issue #XXXX (replace XXXX with an open issue number)

#### Description <!-- Describe your changes in detail --> The main reason for these changes is that we haven't found any possibility to distinguish which of `fr` timeouts expires. The rest of the logs are also helpful, but secondary. As they all are under `ifdef TIMEOUT_DEBUG` I hope it is not a big deal. You can view, comment on, or merge this pull request online at:

https://github.com/kamailio/kamailio/pull/2818

-- Commit Summary --

* tm: enhance fr/retr timers logging

-- File Changes --

M src/modules/tm/t_lookup.c (6) M src/modules/tm/t_reply.c (3) M src/modules/tm/t_suspend.c (3) M src/modules/tm/timer.c (7) M src/modules/tm/timer.h (4)

-- Patch Links --

https://github.com/kamailio/kamailio/pull/2818.patch https://github.com/kamailio/kamailio/pull/2818.diff