fixed coap_iterator_next() to work on utlist structure.
fixed coap_iterator_next() to work on utlist structure.

gebart/libcoap,nmacs/libcoap,gebart/libcoap,sgso/libcoap,thecodemaiden/libcoap-fork,fredericgermain/libcoap,authmillenon/libcoap,fredericgermain/libcoap,nmacs/libcoap,RIOT-OS/libcoap,nmacs/libcoap,thecodemaiden/libcoap-fork,fredericgermain/libcoap,authmillenon/libcoap,sgso/libcoap,RIOT-OS/libcoap,gebart/libcoap,authmillenon/libcoap,sgso/libcoap