connectorConnect() creates a bufio.NewReader to read the HTTP 101
upgrade response, but then passes the raw conn to yamux.Server().
If TCP coalesces the 101 response with initial yamux frames, the
bufio reader over-reads into its buffer and those bytes are lost
to yamux, causing session failure.
Wrap the bufio.Reader and raw conn into a bufferedConn so yamux
reads through the buffer first.
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