connection of a 101 response is never closed #2708

On a 101 Switching Protocols response, Do wraps the body in io.NopCloser and skips the deferred close, so Body.Close() never closes the upgraded connection. It stays open after Do returns (reproduced via common/httpx with upgrade headers); with a zero read limit it is closed.

Reached from the CLI when upgrade headers are sent (e.g. -H "Upgrade: websocket"), one open connection per target. Found in review of #2705.