Xpra: Ticket #2565: set python3 ssl socket timeout

Setting the timeout on a socket wrapped with ssl gives:

Exception in thread new-ssl-connection:
Traceback (most recent call last):
  File "/usr/lib64/python3.7/threading.py", line 926, in _bootstrap_inner
    self.run()
  File "/usr/lib64/python3.7/threading.py", line 870, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib64/python3.7/site-packages/xpra/server/server_core.py", line 1084, in handle_new_connection
    sock.settimeout(self._socket_timeout)
OSError: [Errno 9] Bad file descriptor

So r17028 was skipping ssl sockets.