Bluetooth: Set HCI_PAIRABLE during power on for legacy ioctl

When the controller is brought up using legacy ioctl, the setting of
the HCI_PAIRABLE flag should happen then. Previously it was set during
enumeration and when retrieving device information.

This change also will not set the HCI_PAIRABLE flag when the controller
is used with the HCI User Channel operation.

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