Iperf3/Iperf2 please support SSH/TLS encryption.

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# Context

* Version of iperf3:

* Hardware:

* Operating system (and distribution, if any):
Windows 10 & Debian 10
_Please note: iperf3 is supported on Linux, FreeBSD, and macOS.
Support may be provided on a best-effort basis to other UNIX-like
platforms. We cannot provide support for building and/or running
iperf3 on Windows, iOS, or Android._

* Other relevant information (for example, non-default compilers,
libraries, cross-compiling, etc.):

_Please fill out one of the "Bug Report" or "Enhancement Request"
sections, as appropriate._

# Bug Report

* Expected Behavior
Iperf3/Iperf2 please supports SSH/TLS encryption, like Rsync. This can test encryption performance. Rsync supports SSH with OpenSSH, and TLS with stunnel. See `man rsync`. Use `scp -v -o UserKnownHostsFile=/dev/null /dev/zero root@localhost:/dev/null` will return error.
* Actual Behavior

* Steps to Reproduce

* Possible Solution

_Please submit patches or code changes as a pull request._

# Enhancement Request

* Current behavior

* Desired behavior

* Implementation notes
Windows 10 includes OpenSSH.
https://winscp.net/eng/docs/guide_windows_openssh_server
_If submitting a proposed implementation of an enhancement request,
please use the pull request mechanism._

The request concerns iperf3/iperf2 and compares rsync with OpenSSH and stunnel, but it names no source files, tests, or implementation entry points. Start by mapping the existing transport and protocol handling, then determine how SSH and TLS support would be scoped; done should include encrypted performance testing for the requested modes.

Written by the indexing model from the issue text.