netutils/er-coap: add to support TCP/TLS as per the RFC

netutils/er-coap: add to support TCP/TLS as per the RFC

RFC reference : https://tools.ietf.org/html/draft-ietf-core-coap-tcp-tls-02
 - patch is available from https://github.com/artikcloud/artikcloud-lwm2m-c
 - Author: Gregory Lemercier <g.lemercier@samsung.com>

Implementation required the following modifications:
 - Passing the token as an argument to the registration frame
 - Implementation of the "nibble" variable length header in CoAP
   for TCP as detailed in the current draft of the specification.
   Note that this might change later as the RFC undergoes changes

Change-Id: Ie94defbc30272c6a1e88c09dc246ebfd09d3bb48
Signed-off-by: Jin-Seong Kim <jseong82.kim@samsung.com>