Avoid child process become zombie, and some code cleanup.

DONE:
  * SCTP multi-stream RPC service support.
  * SCTP RPC client support.
  * Test cases.

TODO:
  * SCTP message based send/receive.
  * Potential crashes.
  * Memory leak.
  * Server keep connection even if client disconnected.
  * Implement SCTP keep-alive.