Bluetooth: Add reading of page scan parameters

These parameters are related to the "fast connectable" mode that can be
changed through the mgmt interface. Not all controllers properly reset
these values with HCI_Reset so they need to be read in order to be able
to verify whether the values are correct or not before enabling page
scan.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>