Add agent.h and agent.c to deal with some common agent job:
- checking message from network and fixing network order.
- send back file transfer status.
Code based on Linux agent and Windows agent.
AgentXxxx and agent_xxx are used to avoid conflicts with protocol.
See agent.h for more detail on how to use these APIs.
Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
