Bluetooth: fix locking in hci_conn_request_evt() with HCI_PROTO_DEFER

Bluetooth: fix locking in hci_conn_request_evt() with HCI_PROTO_DEFER

When protocol sets HCI_PROTO_DEFER, hci_conn_request_evt() calls
hci_connect_cfm(conn) without hdev->lock. Generally hci_connect_cfm()
assumes it is held, and if conn is deleted concurrently -> UAF.

Only SCO and ISO set HCI_PROTO_DEFER and only for defer setup listen,
and HCI_EV_CONN_REQUEST is not generated for ISO.  In the non-deferred
listening socket code paths, hci_connect_cfm(conn) is called with
hdev->lock held.

Fix by holding the lock.

Fixes: 70c464256310 ("Bluetooth: Refactor connection request handling")
Signed-off-by: Pauli Virtanen <pav@iki.fi>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>