Bluetooth: Temporary keys should be retained during connection

If a key is non persistent then it should not be used in future
connections but it should be kept for current connection. And it
should be removed when connecion is removed.

Signed-off-by: Vishal Agarwal <vishal.agarwal@stericsson.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>