test: add test for protocol header

[ViolaPioggia]

What type of PR is this?

test

(Optional) Translate the PR title into Chinese.

增加 pkg/protocol/header.go的单测覆盖率 到 90%

(Optional) More detail description for this PR(en: English/zh: Chinese).

en: Increase the single test coverage of 'pkg/protocol/header. go' to 90%
zh(optional): 增加 pkg/protocol/header.go的单测覆盖率 到 90%

(Optional) Which issue(s) this PR fixes:

part of #257

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +0.20% 🎉

Comparison is base (61573bd) 79.87% compared to head (f53a541) 80.07%.

❗ Current head f53a541 differs from pull request most recent head b805ca8. Consider uploading reports for the commit b805ca8 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #869      +/-   ##
===========================================
+ Coverage    79.87%   80.07%   +0.20%     
===========================================
  Files           97       97              
  Lines         9598     9598              
===========================================
+ Hits          7666     7686      +20     
+ Misses        1432     1421      -11     
+ Partials       500      491       -9     

see 3 files with indirect coverage changes

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[welkeyever]

LGTM, thx~