Implement of RPC keep-alive, also detect abnormal disconnect from client.

    DONE:
      * SCTP multi-stream RPC service support.
      * SCTP RPC client support.
      * Implement RPC keep-alive for SCTP/TCP.
      * Test cases.

    TODO:
      * SCTP message based send/receive.
      * Potential crashes.
      * Memory leak.