Add prepareSecure method to tcpsocket

Add prepareSecure method to tcpsocket, to fix https://github.com/uProxy/uproxy/issues/413. In freedom-for-chrome, this will call .setPaused, but in freedom-for-firefox and node this will be a no-op
can a check be added to see if the socket has been paused to let the user know they've failed to 'prepareSecure'?