samples: lwm2m: Add docker test script

Add test script that uses same configuration that the
interoperability test.

This is only checking that unsecure client registers and
responds to a GET query.

Signed-off-by: Seppo Takalo <seppo.takalo@nordicsemi.no>

samples/net/lwm2m_client/docker-test.sh

@@ -0,0 +1,29 @@
+# Copyright (c) 2023 Nordic Semiconductor ASA
+# SPDX-License-Identifier: Apache-2.0
+
+if [ -z "$RUNNING_FROM_MAIN_SCRIPT" ]; then
+    echo "Do not run this script directly!"
+    echo "Run $ZEPHYR_BASE/scripts/net/run-sample-tests.sh instead."
+    exit 1
+fi
+
+IP="--ip=192.0.2.2 --ip6=2001:db8::2"
+FWD="-p 8080:8080 -p 8081:8081 -p 5683:5683/udp"
+
+start_configuration "$IP $FWD" || return $?
+start_docker "/net-tools/start-leshan.sh" || return $?
+
+start_zephyr
+
+sleep 5
+curl -s -X GET 'http://localhost:8080/api/clients/native_posix/3/0/0' | grep Zephyr 2>&1 >/dev/null
+result=$?
+
+stop_zephyr
+stop_docker
+
+if [ $result -eq 0 ]; then
+        return 0
+else
+        return 1
+fi