Add set_slave_only method to PtpInstance

[bhagen55]

It can be useful to configure a port's slave_only configuration on the fly. For example, a port might need to start out in slave_only = true while it waits for it's PHC clock to synchronize for hardware timestamping to be reliable. After health checks pass, it can set slave_only = false and become a master if applicable.

I made a small change to add a set_slave_only function to the default dataset, but that wasn't quite enough since the code currently assumes slave_only is set during init and won't change. The largest change is in set_recommended_port_state which will no longer error out if a port is a master with slave_only set. Instead, it will be forced to PortState::Listening like other port states already are.

I'll admit I don't have a wide enough knowledge of the codebase to know if this is all that is needed for this change to work. I added a few unit tests that seem to show it does, but my confidence level isn't super high still. I did test this practically on the bench and it appears to function as intended.

Resolves #799

[codecov]

Codecov Report

❌ Patch coverage is 98.64865% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 63.82%. Comparing base (fe98d5d) to head (e6aee01).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
statime/src/port/bmca.rs	98.38%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #801      +/-   ##
==========================================
+ Coverage   63.64%   63.82%   +0.18%     
==========================================
  Files          62       62              
  Lines        7950     8020      +70     
==========================================
+ Hits         5060     5119      +59     
- Misses       2890     2901      +11     

Flag	Coverage Δ
fuzz	14.68% <0.00%> (-0.04%)	⬇️
fuzz-message_sound	14.68% <0.00%> (-0.04%)	⬇️

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[davidv1992]

Thank you for contributing this. This looks like a very good idea, and with how the codebase works this is the correct approach.