Open the session using the provided
fd socket file descriptor.
This is useful if you create the fd yourself, for example to setup a SSH tunnel.
Note however that additional sockets will be needed by all the channels created for this so users of this API
should hook into SpiceChannel:
SpiceSession:open-fd signal for each channel they are interested in, and create and pass a new
socket to the channel using open_fd, in the signal callback.
fd is -1, a valid fd will be requested later via the SpiceChannel:
SpiceSession:open-fd signal. Typically, you
would want to just pass -1 as
fd this call since you will have to hook to SpiceChannel:
a file descriptor (socket) or -1
true on success.