Fix a code cleanup.

DHT.c:
- get_close_nodes():
    - be consequent when testing for NULLed results, pack nodes_list dense
    - (logging) dump number of found entries from assoc
- returnedip_ports():
    - fix code cleanup, source is not a valid IP for nodeclient_id

assoc.c:
- Assoc_get_close_entries(): break from loops as soon as a marking-invalid-node is hit