Bluetooth: mgmt: Dequeue pending mesh_send_sync entries on cancel

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: mgmt: Dequeue pending mesh_send_sync entries on cancel In send_cancel(), pending mesh_tx objects are removed from the hdev->mesh_pending list and freed via mesh_send_complete(). However, if a mesh transmission was already queued onto hdev->cmd_sync_work_list via mesh_next(), the queued entry retains a raw pointer to mesh_tx. When hci_cmd_sync_work later processes the entry, it attempts to execute mesh_send_sync and its destroy callback mesh_send_start_complete using the already freed mesh_tx pointer, leading to a use-after-free. Fix this by invoking hci_cmd_sync_dequeue() for mesh_send_sync on the target mesh_tx before completing it. If the entry is found and dequeued, its destroy callback will complete and free the object; otherwise, mesh_send_complete() is called directly. Additionally, ensure the transmission queue advances after cancellation or errors. In mesh_send_start_complete(), call mesh_next() on error unless err is -ECANCELED, because hci_cmd_sync_dequeue() holds hdev->cmd_sync_work_lock and calling mesh_next() synchronously would deadlock. Instead, advance the queue in send_cancel() once the lock is released and if no transmission is in progress.