[PATCH] USBATM: allow isochronous transfer

While the usbatm core has had some support for using isoc urbs
for some time, there was no way for users to turn it on.  While
use of isoc transfer should still be considered experimental, it
now works well enough to let users turn it on.  Minidrivers signal
to the core that they want to use isoc transfer by setting the new
UDSL_USE_ISOC flag.  The speedtch minidriver gets a new module
parameter enable_isoc (defaults to false), plus some logic that
checks for the existence of an isoc receive endpoint (not all
speedtouch modems have one).

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