Fix pfx dedup and add tests

[taktv6]

No description provided.

[codecov-io]

Codecov Report

Merging #233 into master will increase coverage by 0.33%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #233      +/-   ##
==========================================
+ Coverage   57.53%   57.87%   +0.33%     
==========================================
  Files         141      141              
  Lines        7701     7701              
==========================================
+ Hits         4431     4457      +26     
+ Misses       3093     3066      -27     
- Partials      177      178       +1

Impacted Files	Coverage Δ
net/prefix.go	85.15% <0%> (+3.12%)	⬆️
net/ip.go	100% <0%> (+2.85%)	⬆️
net/ip_cache.go	100% <0%> (+64.28%)	⬆️
net/prefix_cache.go	100% <0%> (+64.28%)	⬆️

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[czerwonk]

LGTM