websocket: unexpected reserved bits

I've tested version 2021.2.5 and 2021.3.0

I see this when attempting a `git clone` over ssh
it proceeds a few MB and then hangs up.

client:
```
...
debug2: channel 0: window 1982464 sent adjust 114688 KiB/s
debug2: channel 0: window 1982464 sent adjust 114688 KiB/s
2021-03-15T21:19:27Z DBG backendConn to conn copy: websocket: unexpected reserved bits 0x50
ssh_dispatch_run_fatal: Connection to UNKNOWN port 65535: message authentication code incorrect
fatal: the remote end hung up unexpectedly
fatal: early EOF
fatal: index-pack failed
```

server:
```
...
{"level":"debug","time":"2021-03-15T21:18:21Z","message":"CF-RAY: 6308c61679f8409c-LHR Serving with ingress rule 0"}
{"level":"debug","time":"2021-03-15T21:18:21Z","message":"CF-RAY: 6308c61679f8409c-LHR Request content length 0"}
{"level":"debug","time":"2021-03-15T21:19:27Z","message":"conn to backendConn copy: EOF"}
{"level":"debug","time":"2021-03-15T21:19:27Z","message":"CF-RAY: 6308c61679f8409c-LHR Status: 101 Switching Protocols served by ingress 0"}
{"level":"debug","time":"2021-03-15T21:19:27Z","message":"CF-RAY: 6308c61679f8409c-LHR Response Headers map[Connection:[Upgrade] Sec-Websocket-Accept:[qlvIRCtygLgl6HdcErFevBU/JJ8=] Upgrade:[websocket]]"}
{"level":"debug","time":"2021-03-15T21:19:27Z","message":"CF-RAY: 6308c61679f8409c-LHR Response content length unknown"}
```

could this be a websocket data race issue?