Fix TR logging when cqhv field is absent

[srijeet0406]

This PR is not related to any issue. It adds the "-" default value for the "cqhv" field, when it is absent.

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Which Traffic Control components are affected by this PR?

• Traffic Router

What is the best way to verify this PR?

Make sure all the tests pass.
Send in a request with the protocol set to null or an empty string and make sure the logs show cqhv="-".

If this is a bugfix, which Traffic Control versions contained the bug?

• master

PR submission checklist

• This PR has tests
• This PR has documentation
• This PR has a CHANGELOG.md entry
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

[codecov]

Codecov Report

Merging #7340 (680931c) into master (9da78ae) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #7340   +/-   ##
=========================================
  Coverage     25.02%   25.02%           
  Complexity       98       98           
=========================================
  Files           593      593           
  Lines         73528    73528           
  Branches         90       90           
=========================================
  Hits          18398    18398           
  Misses        53383    53383           
  Partials       1747     1747           

Flag	Coverage Δ
traffic_router_unit	29.03% <ø> (ø)

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[zrhoffman]

Looks good!