Bluetooth: Store current LE connection parameters in hci_conn struct

The LE connection parameters are needed later on to be able to decide
if it is required to trigger connection update procedures. So when the
connection has been established successfully, store the current used
parameters in hci_conn struct.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>