Bluetooth: Track LE connection parameter update event

When the LE controller changes its connection parameters, it will send
a connection parameter update event. Make sure that the new set of
parameters are stored in hci_conn struct and thus will properly update
the previous values retrieved from the connection complete event.

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