Bluetooth: conn: check k_work_submit() retcode

We still don't know how to handle it but at least it's checked now.

(cherry picked from commit 24c7ad3)

Original-Signed-off-by: Jonathan Rico <jonathan.rico@nordicsemi.no>
GitOrigin-RevId: 24c7ad3
Change-Id: I9e076373cf60fc2ac3a8bdefd5f3b1ce6955088a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5516682
Reviewed-by: Ting Shen <phoenixshen@chromium.org>
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>
Commit-Queue: Ting Shen <phoenixshen@chromium.org>
Tested-by: Ting Shen <phoenixshen@chromium.org>

subsys/bluetooth/host/conn.c

@@ -387,16 +387,20 @@ static void wait_for_tx_work(struct bt_conn *conn)
 		tx_notify(conn);
 	} else {
 		struct k_work_sync sync;
+		int err;
 
 		/* API docs mention undefined behavior if syncing on work item
 		 * from wq execution context.
 		 */
 		__ASSERT_NO_MSG(k_current_get() !=
 				k_work_queue_thread_get(&k_sys_work_q));
 
-		k_work_submit(&conn->tx_complete_work);
+		err = k_work_submit(&conn->tx_complete_work);
+		__ASSERT(err >= 0, "couldn't submit (err %d)", err);
+
 		k_work_flush(&conn->tx_complete_work, &sync);
 	}
+	LOG_DBG("done");
 #else
 	ARG_UNUSED(conn);
 #endif	/* CONFIG_BT_CONN_TX */