Fix: Remove udp connection twice(#1297)

[Ovear]

Fix #1297

[codecov-commenter]

Codecov Report

Merging #1305 (c6a4e3a) into master (deb9d08) will decrease coverage by 0.09%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #1305      +/-   ##
==========================================
- Coverage   44.64%   44.54%   -0.10%     
==========================================
  Files         485      485              
  Lines       29534    29540       +6     
==========================================
- Hits        13184    13158      -26     
- Misses      14945    14971      +26     
- Partials     1405     1411       +6     

Impacted Files	Coverage Δ
app/proxyman/inbound/worker.go	37.15% <0.00%> (-0.91%)	⬇️
transport/internet/udp/dispatcher.go	64.76% <0.00%> (-12.39%)	⬇️
common/buf/reader.go	82.35% <0.00%> (-5.89%)	⬇️
proxy/freedom/freedom.go	45.00% <0.00%> (-4.00%)	⬇️
transport/internet/websocket/connection.go	16.51% <0.00%> (-3.67%)	⬇️
transport/pipe/impl.go	87.87% <0.00%> (-2.03%)	⬇️
common/drain/drainer.go	72.41% <0.00%> (+6.89%)	⬆️

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[xiaokangwang]

Thank for your explanation. I have understood the root cause of this error, and I agree with the way this issue is addressed.

The connID(Connection identifier ,app/proxyman/inbound/worker.go:type connID struct) use the connection source and destination to identify different connections. When a inactive connection is removed for inactivity, the new connection that is created later may also be removed as the transport connection is terminate. In this way, the new transport connection and tracked active connection get removed unnecessarily.

This pull request is ready to be merged.

Thanks for your contribution.