The CoAP test server runs in Zephyr and it receives CoAP messages
sent by coap client. The server can receive both plain or DTLS
encrypted CoAP messages. The server has various resource plugins
available but currently activates only three that are needed
by coap-client tester.
Change-Id: I6465a3a057eaf8b412699bba57bf7213548f0377
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>