support ipv6 ipset

[wolf-joe]

for #33

[codecov-commenter]

Codecov Report

Merging #46 (3ad68e8) into master (091062b) will decrease coverage by 0.25%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master      #46      +/-   ##
==========================================
- Coverage   75.17%   74.92%   -0.26%     
==========================================
  Files          12       13       +1     
  Lines        1265     1284      +19     
==========================================
+ Hits          951      962      +11     
- Misses        287      291       +4     
- Partials       27       31       +4     

Impacted Files	Coverage Δ
outbound/groups.go	22.62% <31.81%> (+1.86%)	⬆️
outbound/ipset.go	40.00% <40.00%> (ø)

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