expanded Client_data to hold two addresses (IPv4, IPv6) instead of one

Compilerflag: CLIENT_ONETOONE_IP (to define in DHT.h, default unset i.e. current one address)

Every function in DHT.c working on Client_data has been rewritten to store IPv4 addresses in assoc4, IPv6 addresses in assoc6.
Loading/Storing of states defined with other compiler switch is transparently adjusting to the differences.