bugfix: use header format from coap-17 in hnd_get_time()
bugfix: use header format from coap-17 in hnd_get_time()

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