Test bugfix: close the listener socket that was left open after exitting the function.

[ethouris]

1. The locally created socket for listening has been closed. The socket left open has made the port kept busy and caused other tests to fail.
2. Added extra checks for the test so that SRT functions, if they fail unexpectedly, got also their error displayed in the test.

[codecov-commenter]

Codecov Report

Merging #2538 (d24111c) into master (e082f30) will increase coverage by 1.38%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2538      +/-   ##
==========================================
+ Coverage   64.81%   66.20%   +1.38%     
==========================================
  Files         100      100              
  Lines       19759    19766       +7     
==========================================
+ Hits        12807    13086     +279     
+ Misses       6952     6680     -272     

Impacted Files	Coverage Δ
test/test_bonding.cpp	98.42% <100.00%> (+4.73%)	⬆️
srtcore/packet.cpp	44.04% <0.00%> (-1.91%)	⬇️
srtcore/queue.cpp	81.34% <0.00%> (-0.30%)	⬇️
srtcore/buffer_rcv.cpp	59.02% <0.00%> (+0.19%)	⬆️
srtcore/congctl.cpp	81.34% <0.00%> (+0.51%)	⬆️
srtcore/api.cpp	54.43% <0.00%> (+1.14%)	⬆️
srtcore/core.cpp	60.54% <0.00%> (+1.41%)	⬆️
srtcore/buffer_snd.cpp	67.10% <0.00%> (+1.95%)	⬆️
srtcore/group.h	61.22% <0.00%> (+2.04%)	⬆️
srtcore/cache.h	83.07% <0.00%> (+3.07%)	⬆️
... and 5 more

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