use a buffer from the pool for composing Retry packets

[marten-seemann]

No description provided.

[codecov]

Codecov Report

Merging #2934 (019850e) into master (deacefd) will decrease coverage by 0.04%.
The diff coverage is 42.86%.

@@            Coverage Diff             @@
##           master    #2934      +/-   ##
==========================================
- Coverage   86.22%   86.18%   -0.04%     
==========================================
  Files         132      132              
  Lines        9141     9144       +3     
==========================================
- Hits         7881     7880       -1     
- Misses        910      913       +3     
- Partials      350      351       +1     

Impacted Files	Coverage Δ
server.go	82.30% <42.86%> (-0.98%)	⬇️

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