We emulate the DJ functionality through the driver.

The receiver supports "fake device arrival" which behaves
like the probing of DJ devices.

A non-unifying receiver has 2 USB interfaces, the first one generates
standard keypresses and is compatible with the USB Keyboard Boot Subclass.
The second interface sends events for the mouse and special keys such as
the consumer-page keys. Events are split this way for BIOS / Windows /
generic-hid driver compatibility. This split does not actually match with
which device the event originate from, e.g. the consumer-page key events
originate from the keyboard but are delivered on the mouse interface.

To make sure the events are actually delivered to the dj_device
representing the originating device, we pick which dj_dev to forward
a "regular" input-report to based on the report-number, rather
then based on the originating interface.

Co-authored-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>