Bluetooth: Update page scan when necessary for Add/Remove Device

When we're removing the last item in the white list or adding the first
one to it and HCI_CONNECTABLE is not set we need to update the current
page scan. This patch adds a simple helper function for the purpose and
calls it from the respective mgmt command handlers.

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