USB: Interface Association Descriptors added to CDC & RNDIS

Without Interface Association Descriptor, the CDC serial and
RNDIS functions did not work correctly when added to a
composite gadget with other functions.  This is because, it
defined two interfaces and some hosts tried to treat each
interface separatelly.

Signed-off-by: Michal Nazarewicz <m.nazarewicz@samsung.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>