net: lwm2m: correct packet pending process in lwm2m_send_message()

During the CoAP API change, the way packets were ref'd and then
unref'd in order to stop the packet sending functions from releasing
the net_pkts was changed and never updated in the LwM2M library.

Let's use coap_pending_cycle() and coap_pending_clear() to do the
ref/unref the same way as the coap-client samples in order to
match the pending process with the current CoAP APIs.

Signed-off-by: Michael Scott <michael@opensourcefoundries.com>

subsys/net/lib/lwm2m/lwm2m_engine.c

@@ -1032,41 +1032,44 @@ cleanup:
 int lwm2m_send_message(struct lwm2m_message *msg)
 {
 	int ret;
-	struct net_pkt *pkt;
 
 	if (!msg || !msg->ctx) {
 		SYS_LOG_ERR("LwM2M message is invalid.");
 		return -EINVAL;
 	}
 
-	/* protect the packet from being released inbetween net_app_send_pkt()
+	if (msg->type == COAP_TYPE_CON) {
-	 * to coap_pending_cycle()
+		/*
-	 */
+		 * Increase packet ref count to avoid being unref after
-	pkt = msg->cpkt.pkt;
+		 * net_app_send_pkt()
-	net_pkt_ref(pkt);
+		 */
+		coap_pending_cycle(msg->pending);
+	}
 
 	msg->send_attempts++;
 	ret = net_app_send_pkt(&msg->ctx->net_app_ctx, msg->cpkt.pkt,
 			       &msg->ctx->net_app_ctx.default_ctx->remote,
 			       NET_SOCKADDR_MAX_SIZE, K_NO_WAIT, NULL);
 	if (ret < 0) {
-		goto out;
+		if (msg->type == COAP_TYPE_CON) {
+			coap_pending_clear(msg->pending);
+		}
+
+		return ret;
 	}
 
 	if (msg->type == COAP_TYPE_CON) {
+		/* don't re-queue the retransmit work on retransmits */
 		if (msg->send_attempts > 1) {
-			goto out;
+			return 0;
 		}
 
-		coap_pending_cycle(msg->pending);
 		k_delayed_work_submit(&msg->ctx->retransmit_work,
 				      msg->pending->timeout);
 	} else {
 		lwm2m_reset_message(msg, true);
 	}
 
-out:
-	net_pkt_unref(pkt);
 	return ret;
 }