Gracefully handle missing Baudrate setting in DCF

[acolomb]

The CiA306 spec is not quite clear on which fields are mandatory within the DeviceComissioning section. Thus it should be assumed that the two options handled here could be missing. Instead of raising an exception, ignore the absence of the Baudrate setting.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 67.82%. Comparing base (6a4ca11) to head (96b2f0c).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #492      +/-   ##
==========================================
- Coverage   67.84%   67.82%   -0.03%     
==========================================
  Files          26       26              
  Lines        3107     3108       +1     
  Branches      524      525       +1     
==========================================
  Hits         2108     2108              
  Misses        859      859              
- Partials      140      141       +1     

Files	Coverage Δ
canopen/objectdictionary/eds.py	83.66% <50.00%> (-0.25%)	⬇️

[erlend-aasland]

I added tests for this:

• Add tests for bitrate parsing in import_eds() #495