Draft: openssh mux server support
Add a description of the new feature/bug fix. Reference any relevant bugs.
Checklist
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Commits have Signed-off-by:with name/author being identical to the commit author
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Code modified for feature 
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Test suite updated with functionality tests 
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Test suite updated with negative tests 
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Documentation updated 
Reviewer's checklist:
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Any issues marked for closing are addressed 
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There is a test suite reasonably covering new functionality or modifications 
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Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTING.md 
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This feature/change has adequate documentation added 
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No obvious mistakes in the code