server side external io api logic broken

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currently impossible to override io.TransportAttach because ->context->rdp->transport is available only after freerdp_peer_context_new call, but inside of freerdp_peer_context_new transport_attach is called before any chance to override it, it is possible to create own implementation of freerdp_peer_context_new, but it will also add requirement for implementation of lot freerdp internals which is undesired and should be avoided if possible.

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also looks like some in some other places file descriptor used directly in server side (peer) code

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looks like another task for me (. ok, i am on it.

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https://github.com/FreeRDP/FreeRDP/pull/6668 - started work here