detect network change on Mac Catalina

[richardschneider]

Only do magic from @eshvatskyi on Windows. Removing/Adding event handler causes
infinitive recursion on Catalina. See #87

[codecov-io]

Codecov Report

Merging #89 into master will increase coverage by 0.59%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #89      +/-   ##
==========================================
+ Coverage   90.52%   91.11%   +0.59%     
==========================================
  Files          10       10              
  Lines         517      518       +1     
==========================================
+ Hits          468      472       +4     
+ Misses         49       46       -3

Impacted Files	Coverage Δ
src/MulticastService.cs	91.57% <100%> (+0.04%)	⬆️
src/MulticastClient.cs	85.24% <0%> (+2.45%)	⬆️

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[richardschneider]

@eshvatskyi are you happy with this?

[eshvatskyi]

@eshvatskyi are you happy with this?
I'm sorry, but I didn't get, is this an irony, Catalina just launched, and it looks, has more bugs than windows )), don't claim me ))