Bluetooth: Create hci_req_add_le_passive_scan helper

This patches creates the public hci_req_add_le_passive_scan helper so
it can be re-used outside hci_core.c in the next patch.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Update background scan parameters

If new scanning parameters are set while background scan is running,
we should restart background scanning so these parameters are updated.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>