[WIP] Fix goroutine leakage

[enobufs]

Description

• Added reproducible leakage check along with a fix.
• Fixed a test case that had a goroutine that did not exit.
• Ubuntu linux appears to have a bug causing initial packet exchange to fail (see issue Flaky tests and/or goroutine leaks #270 for details). To workaround it, the test tool createAssocs() has been updated to use "dumbConn2" (similar to the existing "dumbConn" which uses test.Bridge.) instead of using kernel routing between the two net.Conn endpoints.

Reference issue

Fixes #270

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1abdf2d) 67.23% compared to head (91bc4b1) 80.53%.

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #292       +/-   ##
===========================================
+ Coverage   67.23%   80.53%   +13.29%     
===========================================
  Files          48       48               
  Lines        4047     4053        +6     
===========================================
+ Hits         2721     3264      +543     
+ Misses       1172      647      -525     
+ Partials      154      142       -12     

Flag	Coverage Δ
go	80.53% <100.00%> (?)
wasm	67.18% <33.33%> (-0.06%)	⬇️

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