UEAGLE: Allow user to choose input interface alternate setting

Let's user control how much USB bus bandwidth will be reserved by
ueagle-atm device. This make possible to share bus with other devices
when ueagle-atm driver works in isochronous mode.

Signed-off-by: Stanislaw Gruszka <stf_xl@wp.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>