Feat: add sniffing for TUN

[AkinoKaede]

No description provided.

[codecov-commenter]

Codecov Report

Attention: 16 lines in your changes are missing coverage. Please review.

Comparison is base (f8d2741) 37.69% compared to head (a96d343) 37.71%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2733      +/-   ##
==========================================
+ Coverage   37.69%   37.71%   +0.01%     
==========================================
  Files         659      659              
  Lines       38874    38890      +16     
==========================================
+ Hits        14653    14666      +13     
- Misses      22606    22612       +6     
+ Partials     1615     1612       -3     

Files	Coverage Δ
app/tun/config.pb.go	19.80% <0.00%> (-0.82%)	⬇️
app/tun/handler_tcp.go	0.00% <0.00%> (ø)
app/tun/handler_udp.go	0.00% <0.00%> (ø)

... and 5 files with indirect coverage changes

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[xiaokangwang]

Nice! No issue was discovered, it will be included in v5.11.0 . Could you by the way work on getting its document updated now? I can write it, but it seems others don't feel the same when I think it is easy to understand.