Add missing inline

[streeve]

Mistake from #395

Fixes #423

[codecov]

Codecov Report

Merging #424 (581f516) into master (3de8037) will not change coverage.
The diff coverage is 100.0%.

@@          Coverage Diff           @@
##           master    #424   +/-   ##
======================================
  Coverage    93.0%   93.0%           
======================================
  Files          37      37           
  Lines        4269    4269           
======================================
  Hits         3973    3973           
  Misses        296     296           

Impacted Files	Coverage Δ
core/src/Cabana_CommunicationPlan.hpp	95.6% <100.0%> (ø)

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