Fix DSCP detection on Windows. Add DSCP support to SecNetPerf

[anrossi]

Description

DSCP detection on Windows was incorrect and setting an invalid value, which would always error, causing MsQuic to determine DSCP to not be supported. This change fixes that bug, and also adds support to SecNetPerf to set DSCP on outgoing packets. It also adds support for receiving DSCP to the Windows datapath layers, which enables the DSCP tests to function.

Testing

Updated existing DSCP tests to validate DSCP is getting sent and received as expected.

Documentation

SecNetPerf help text was updated to list the new option.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.15%. Comparing base (2e4a9f0) to head (d87bbe2).
Report is 18 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5130      +/-   ##
==========================================
- Coverage   87.45%   86.15%   -1.30%     
==========================================
  Files          59       59              
  Lines       18048    18086      +38     
==========================================
- Hits        15783    15582     -201     
- Misses       2265     2504     +239     

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[sm-msft]

Suggest updating the readme file with help and sample test run data: https://github.com/microsoft/msquic/blob/main/src/perf/readme.md

[nibanks]

TODO: Tests should be updated/verified to be checking for DSCP

Do you plan to fix this up soon? We need to get this into the release/2.5 branch.

[anrossi]

TODO: Tests should be updated/verified to be checking for DSCP

Do you plan to fix this up soon? We need to get this into the release/2.5 branch.

Ah the problem is that, on receive, windows doesn't fetch the IP_TOS field, just ECN, so this test is failing because now it's actually testing DSCP, and we weren't fetching the DSCP values.
I'd added fetch support for DSCP, which should work downlevel since it has been around for a while.