[winswitch] Disable TCP on systemd socket activation

[Antoine Martin]

(..)
> I tested the 4.1 beta packages and the feature works as intended, but I
> am unable to login to a session.
> 
> I only appended XPRA_SD_SOCKET_TYPE=wss to /etc/sysconfig/xpra and
> restarted xpra.
> 
> HTTP connections are dropped. HTTPS connections succeed.
That's expected: the socket is now SSL enabled (wss) and it will reject
non-ssl traffic.

> Attempting to login results in an authentication failure. Logs show:
> 
> Error: the proxy server requires an authentication mode,
> client connection 'wss' does not specify one
> use 'none' to disable authentication
> 
> Removing the new environment variable from /etc/sysconfig/xpra and a
> service restart allows me to login.
Try replacing "--tcp-auth=$TCP_AUTH" with "--wss-auth=sys"

We could make this the default too I guess - though it may be confusing
to see an auth option defined for a socket type that isn't used by default.

Cheers,
Antoine

> 
> Thanks,
> Michael