Remove one alloc on subprotocol selection

[FZambia]

Removing one alloc on strings.Split.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.61%. Comparing base (be9c49f) to head (1dd3f20).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #476      +/-   ##
==========================================
+ Coverage   83.51%   83.61%   +0.09%     
==========================================
  Files          39       39              
  Lines        9041     9041              
==========================================
+ Hits         7551     7560       +9     
+ Misses       1128     1120       -8     
+ Partials      362      361       -1     

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