Bluetooth: clear the temporary linkkey in hci_conn_cleanup

Bluetooth: clear the temporary linkkey in hci_conn_cleanup

If a hardware error occurs and the connections are flushed without a
disconnection_complete event being signaled, the temporary linkkeys are
not flushed.

This change ensures that any outstanding flushable linkkeys are flushed
when the connection are flushed from the hash table.

Additionally, this also makes use of test_and_clear_bit to avoid
multiple attempts to delete the link key that's already been flushed.

Signed-off-by: Alain Michaud <alainm@chromium.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>