Bluetooth: hci_sync: Avoid use-after-free in dbg for hci_remove_adv_monitor()

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: hci_sync: Avoid use-after-free in dbg for hci_remove_adv_monitor() KASAN reports that there's a use-after-free in hci_remove_adv_monitor(). Trawling through the disassembly, you can see that the complaint is from the access in bt_dev_dbg() under the HCI_ADV_MONITOR_EXT_MSFT case. The problem case happens because msft_remove_monitor() can end up freeing the monitor structure. Specifically: hci_remove_adv_monitor() -> msft_remove_monitor() -> msft_remove_monitor_sync() -> msft_le_cancel_monitor_advertisement_cb() -> hci_free_adv_monitor() Let's fix the problem by just stashing the relevant data when it's still valid.