[PATCH] USBATM: change the default speedtouch iso altsetting

The maximum possible bandwidth for a speedtouch modem is about 7Mbaud.
You can only get this by using isochronous urbs (enable_isoc=1) and
altsetting 3.  With the current default altsetting of 2, the modem
maxes out at about 4Mbaud.  So change the default altsetting to 3
when using isochronous urbs.  It would be nice to base the altsetting
on the detected line speed, but that's hard given the current design.

Signed-off-by: Duncan Sands <baldrick@free.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>