io: bind to socket before creating QIOChannelSocket

In the QIOChannelSocket test we create a socket file
descriptor and then try to create a QIOChannelSocket.
This works on Linux, but fails on Win32 because it is
not valid to call getsockname() on an unbound socket.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
