USB: ethernet gadget interop with MCCI Windows driver

It turns out that minor tweaks to the "CDC Subset" support in the Ethernet
gadget driver, just updating a config descriptor, let it be automagically
recognized by a Windows driver supported by MCCI.

This patch adds those descriptors, so systems using PXA 255 processors
(like Gumstix etc) can interop with those commercial MS-Windows drivers.
This is a Good Thing since Microsoft's RNDIS code has bugginess issues,
which are unfortunately compounded by "won't fix" issues as well as "the
published specs are incomplete and wrong" issues.  Being able to talk to
the MCCI driver gives Windows users another connectivity option.  (MCCI
also has CDC Ethernet drivers, which can help most non-PXA processors.)
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>