A relay notifier that observes the underlying endpoint is added as the
notifier for the socket. It broadcasts to its observers when either end
of the channel has IoEvents.
1. Implement type-safe functions;
2. Improve the correctness of nearly all the functions;
3. Improve the readability by introducing Listener and Endpoint for StreamUnix;
4. Substitue RingBuf with Channel in Unix socket.
* Add patch to Rust SGX SDK to enable integrity-only SgxFile
* Upgrade to the new SEFS extended with the integrity-only mode
* Use integrity-only SEFS for /bin and /lib in test
* Add the MAC of integrity-only SEFS to Occlum.json in test
* Mount multiple FS according to Occlum.json
* Check the MACs of integrity-only SEFS images