prop224: Client introduction point establishment
Implement the client introduction point establishment process and logic for proposal 224.
- Pick IP from descriptor.
- Use IP failure cache.
- Open introduction circuit.
- Setup circuit identifier on intro circuit.
- Generate/Send INTRODUCE1 cell.
- Handle INTRODUCE_ACK cell.
In legacy code, see rend_client_send_introduction()
and rend_client_introduction_acked()
in src/or/rendclient.c