Use error code instead of exception in socket shutdown

[qchateau]

By: nsubiron

[codecov-io]

Codecov Report

Merging #11 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master      #11   +/-   ##
=======================================
  Coverage   91.78%   91.78%           
=======================================
  Files          39       39           
  Lines        1108     1108           
=======================================
  Hits         1017     1017           
  Misses         91       91

Impacted Files	Coverage Δ
include/rpc/detail/async_writer.h	40% <100%> (ø)	⬆️

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