Since the local_interface was added to the request handler callback,
the examples rd.c and etsi_iot_01.c were broken. This change fixes
rd.c and abandons etsi_iot_01.c (as it is very outdated).
From jsucaet's error description (Credits to Marc Haesen for revealing this bug):
The intent of the current code of coap_send is to release the allocated
memory upon success and not to release when an error has occured. However
this is broken (returning from coap_send with an error and a deallocated
pdu ptr is possible).
In the patch, I propose to let the calling function (of coap_send) be
responsible for free'ing the allocated pointer.
Olaf Bergmann