[#81] fix signal handler

[elfenpiff]

Notes for Reviewer

The original problem was that I defined a struct sigaction_t in rust posix types and reinterpreted it has the posix c type sigaction, this worked for all platforms, but this was pure luck since posix states nothing about the member order or hidden members. It is not possible to use the sigaction struct directly from bindgen since some libc implementation have weird C macro hacks. So there are posix libc implementations that strictly speaking violate the posix standard and correct this with a macro called sa_handler (the member they renamed to something else).
With bindgen it ends up with different struct member names on different libc implementation therefore, there was nothing else possible but to create an iox2_sigaction struct in posix.h and do the translation in the c function iox2_sigaction_func since C supports these weird macro hacks in a platform independent way.

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1. Add sensible notes for the reviewer
2. PR title is short, expressive and meaningful
3. Relevant issues are linked
4. Every source code file has a copyright header with SPDX-License-Identifier: Apache-2.0 OR MIT
5. Branch follows the naming format (iox2-123-introduce-posix-ipc-example)
6. Commits messages are according to this guideline
   • Commit messages have the issue ID ([#123] Add posix ipc example)
   • Commit author matches Eclipse Contributor Agreement (and ECA is signed)
7. Tests follow the best practice for testing
8. Changelog updated in the unreleased section including API breaking changes
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10. All checks have passed (except task-list-completed)

Checklist for the PR Reviewer

• Commits are properly organized and messages are according to the guideline
• Unit tests have been written for new behavior
• Public API is documented
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Post-review Checklist for the PR Author

1. All open points are addressed and tracked via issues

References

Use either 'Closes #123' or 'Relates to #123' to reference the corresponding issue.

Relates to #81

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1607c02) 78.01% compared to head (9192cad) 78.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #84      +/-   ##
==========================================
- Coverage   78.01%   78.00%   -0.01%     
==========================================
  Files         172      172              
  Lines       18791    18778      -13     
==========================================
- Hits        14659    14647      -12     
+ Misses       4132     4131       -1     

Files	Coverage Δ
iceoryx2-bb/posix/src/signal.rs	85.02% <100.00%> (-0.07%)	⬇️
iceoryx2-pal/posix/src/linux/dirent.rs	100.00% <ø> (ø)
iceoryx2-pal/posix/src/linux/signal.rs	100.00% <100.00%> (ø)
iceoryx2-pal/posix/src/linux/types.rs	100.00% <ø> (ø)

... and 1 file with indirect coverage changes

[elBoberido]

Looks good but I think you mixed up one variable