Port System.Net.Security to OpenBSD

[am11]

Contributes to #124911.

[am11]

@sethjackson, unit tests with this change:

/home/am11/th/artifacts/bin/testhost/net11.0-openbsd-Debug-x64/dotnet exec --runtimeconfig System.Net.Security.Unit.Tests.runtimeconfig.json --depsfile System.Net.Security.Unit.Tests.deps.json xunit.console.dll System.Net.Security.Unit.Tests.dll -xml testResults.xml -nologo -nocolor -notrait category=IgnoreForCI -notrait category=OuterLoop -notrait category=failing
popd
===========================================================================================================
~/system.netsec ~/system.netsec
  Discovering: System.Net.Security.Unit.Tests (method display = ClassAndMethod, method display options = None)
  Discovered:  System.Net.Security.Unit.Tests (found 83 of 86 test cases)
  Starting:    System.Net.Security.Unit.Tests (parallel test collections = on [5 threads], stop on fail = off)
    System.Net.Security.Tests.NegotiateAuthenticationTests.Package_Unsupported_NTLM [SKIP]
      Condition(s) not met: "IsNtlmUnavailable"
    System.Net.Security.Tests.NegotiateAuthenticationTests.NtlmMalformedChallenge_ReturnsInvalidToken [SKIP]
      Condition(s) not met: "UseManagedNtlm"
    System.Net.Security.Tests.NegotiateAuthenticationTests.NtlmWithPreExistingTargetInfoEntriesTest [SKIP]
      Condition(s) not met: "UseManagedNtlm"
  Finished:    System.Net.Security.Unit.Tests
=== TEST EXECUTION SUMMARY ===
   System.Net.Security.Unit.Tests  Total: 114, Errors: 0, Failed: 0, Skipped: 3, Time: 5.449s
~/system.netsec

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[sethjackson]

Nice! Seems you fixed the test failures I was having and makes sense as I didn't do the opt-in to managed NTLM. 💯

[rzikm]

LGTM