Bluetooth: Do not cancel advertising when starting a scan

BlueZ cancels adv when starting a scan, but does not cancel a scan when
starting to adv. Neither is required, so this brings both to a
consistent state (of not affecting each other). Some very rare (I've
never seen one) BT 4.0 chips will fail to do both at once. Even this is
ok since the command that will fail will be the second one, and thus the
common sense logic of first-come-first-served is preserved for BLE
requests.

Signed-off-by: Dmitry Grinberg <dmitrygr@google.com>
Signed-off-by: Manish Mandlik <mmandlik@google.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>