Bluetooth: btusb: Add HCI Drv commands for configuring altsetting

Bluetooth: btusb: Add HCI Drv commands for configuring altsetting

Although commit 75ddcd5ad40e ("Bluetooth: btusb: Configure altsetting
for HCI_USER_CHANNEL") has enabled the HCI_USER_CHANNEL user to send out
SCO data through USB Bluetooth chips, it's observed that with the patch
HFP is flaky on most of the existing USB Bluetooth controllers: Intel
chips sometimes send out no packet for Transparent codec; MTK chips may
generate SCO data with a wrong handle for CVSD codec; RTK could split
the data with a wrong packet size for Transparent codec; ... etc.

To address the issue above one needs to reset the altsetting back to
zero when there is no active SCO connection, which is the same as the
BlueZ behavior, and another benefit is the bus doesn't need to reserve
bandwidth when no SCO connection.

This patch adds "Supported Altsettings" and "Switch Altsetting" commands
that allow the user space program to configure the altsetting freely.

This patch is tested on ChromeOS devices. The USB Bluetooth models
(CVSD, TRANS alt3, and TRANS alt6) could pass the stress HFP test narrow
band speech and wide band speech.

Cc: chromeos-bluetooth-upstreaming@chromium.org
Fixes: b16b327edb4d ("Bluetooth: btusb: add sysfs attribute to control USB alt setting")
Signed-off-by: Hsin-chen Chuang <chharry@chromium.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>