For the userspace it is needed to distinguish between requests for the
control or streaming interface. The userspace would have to parse the
configfs to know which interface index it has to compare the ctrl
requests against. Since the interface numbers are not fixed, e.g. for
composite gadgets, the interface offset depends on the setup.

The kernel has this information when handing over the ctrl request to
the userspace. This patch removes the offset from the interface numbers
and expose the default interface defines in the uapi g_uvc.h.
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Link: https://lore.kernel.org/r/20221011075348.1786897-1-m.grzeschik@pengutronix.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>