net: lwm2m: do not expose security object

According to LwM2M specification 5.2.7.3 Bootstrap DISOCVER,
security object is only reported to the bootstrap server.

Correct the behavior to (1) report server object to the server
(2) do not report security object at registration time

Signed-off-by: Robert Chou <[email protected]>

Author: rbtchc

subsys/net/lib/lwm2m/lwm2m_engine.c

@@ -586,6 +586,11 @@ u16_t lwm2m_get_rd_data(u8_t *client_data, u16_t size)
 	int len;
 
 	SYS_SLIST_FOR_EACH_CONTAINER(&engine_obj_list, obj, node) {
+		/* Security obj MUST NOT be part of registration message */
+		if (obj->obj_id == LWM2M_OBJECT_SECURITY_ID) {
+			continue;
+		}
+
 		len = snprintf(temp, sizeof(temp), "%s</%u>",
 			       (pos > 0) ? "," : "", obj->obj_id);
 		if (pos + len >= size) {
@@ -1816,8 +1821,10 @@ static int do_discover_op(struct lwm2m_engine_context *context)
 	out->outlen += strlen(DISCOVER_PREFACE);
 
 	SYS_SLIST_FOR_EACH_CONTAINER(&engine_obj_inst_list, obj_inst, node) {
-		/* avoid discovery for security and server objects */
-		if (obj_inst->obj->obj_id <= LWM2M_OBJECT_SERVER_ID) {
+		/* TODO: support bootstrap discover
+		 * Avoid discovery for security object (5.2.7.3)
+		 */
+		if (obj_inst->obj->obj_id == LWM2M_OBJECT_SECURITY_ID) {
 			continue;
 		}