refactor: Use strong typedef for network family.

[iphydf]

This change is 

[codecov]

Codecov Report

Attention: Patch coverage is 67.16418% with 22 lines in your changes missing coverage. Please review.

Project coverage is 73.09%. Comparing base (0ec4978) to head (12cfaec).
Report is 20 commits behind head on master.

Files with missing lines	Patch %	Lines
toxcore/network.c	63.93%	22 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2641      +/-   ##
==========================================
- Coverage   73.09%   73.09%   -0.01%     
==========================================
  Files         149      149              
  Lines       30533    30559      +26     
==========================================
+ Hits        22319    22337      +18     
- Misses       8214     8222       +8     

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