USB: gadget rndis: stop windows self-immolation

Somewhere in the conversion of the RNDIS gadget code to the new
framework, the descriptor of its data interface seems to have
been copied from the CDC Ethernet driver.  Unfortunately that
means it got a nonzero altsetting ... which is incorrect.  Issue
uncovered by Richard Röjfors <richard.rojfors@endian.se>.

This patch fixes that problem, and resolves at least some cases
of Windows XP bluescreening itself.

Tested-by: Richard Röjfors <richard.rojfors@endian.se&gt;.>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>