Add simple UDP echo server example

This example used to be considered specific to the CC2538DK platform. However, there was nothing really platform-specific to it. This commit moves the example to the top-level examples directory and documents it.

examples/platform-specific/cc2538dk/udp-ipv6-echo-server/Makefile.target

@@ -1 +0,0 @@
-TARGET = cc2538dk

examples/udp-echo-server/Makefile

@@ -2,6 +2,6 @@ CONTIKI_PROJECT = udp-echo-server
 
 all: $(CONTIKI_PROJECT)
 
-CONTIKI = ../../../..
-CFLAGS += -DUIP_CONF_ND6_SEND_NS=1
+CONTIKI = ../..
+
 include $(CONTIKI)/Makefile.include

examples/udp-echo-server/README.md

@@ -0,0 +1,14 @@
+UDP echo server example
+=======================
+This example demonstrates how to implement a simple UDP-server by
+using the original UDP API (as opposed to using the simple-udp module).
+
+It is anticipated that this example will run on all supported platforms.
+
+To test, compile and programme your device (or execute on the native
+platform). Then you can use netcat, like so:
+
+    $ nc -6u <your device's IPv6 address> 3000
+
+Type something in your console and you should see it echoed back by the
+UDP server running on your device.

examples/udp-echo-server/udp-echo-server.c

@@ -28,18 +28,7 @@
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
  * OF THE POSSIBILITY OF SUCH DAMAGE.
  */
-/** \addtogroup cc2538-examples
- * @{
- *
- * \defgroup cc2538-echo-server cc2538dk UDP Echo Server Project
- *
- *  Tests that a node can correctly join an RPL network and also tests UDP
- *  functionality
- * @{
- *
- * \file
- *  An example of a simple UDP echo server for the cc2538dk platform
- */
+/*---------------------------------------------------------------------------*/
 #include "contiki.h"
 #include "contiki-lib.h"
 #include "contiki-net.h"
@@ -107,7 +96,3 @@ PROCESS_THREAD(udp_echo_server_process, ev, data)
   PROCESS_END();
 }
 /*---------------------------------------------------------------------------*/
-/**
- * @}
- * @}
- */

tests/02-compile-arm-ports/Makefile

@@ -16,7 +16,7 @@ ipv6/rpl-border-router/cc2538dk \
 ipv6/rpl-udp/cc2538dk \
 ipv6/coap-example/cc2538dk \
 ipso-objects/cc2538dk \
-platform-specific/cc2538dk/udp-ipv6-echo-server/cc2538dk \
+udp-echo-server/cc2538dk \
 ipv6/multicast/cc2538dk \
 platform-specific/cc2538-common/cc2538dk \
 platform-specific/cc2538-common/mqtt-demo/cc2538dk \