Bluetooth: Add HCIUARTSETFLAGS and HCIUARTGETFLAGS ioctls

This patch introduces two new ioctls: HCIUARTSETFLAGS and
HCIUARTGETFLAGS. The only flag available for now is HCI_UART_RAW_DEVICE
which allows to initialize a UART device into RAW mode from userspace.
This is particularly useful for experimenting with Bluetooth controllers
that don't yet have proper support in BlueZ.

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