-/* Special function used in libradsec blocking dispatching mode,
- i.e. with socket set to block on read/write and with no libradsec
- callbacks registered.
-
- For any other use of libradsec, a the received_cb callback should
- be registered in the callbacks member of struct rs_connection.
-
- On successful reception of a RADIUS message it will be verified
- against REQ_MSG, if !NULL.
-
- If PKT_OUT is !NULL it will upon return point at a pointer to a
- struct rs_packet containing the message.
-
- If anything goes wrong or if the read times out (TODO: explain),
- PKT_OUT will not be changed and one or more errors are pushed on
- the connection (available through rs_err_conn_pop()). */