USB: gadget: net2280: implement set_wedge

This patch (as1132) implements the set_wedge() method for net2280.
This method is necessary for strict USBCV compliance in
g_file_storage.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: David Brownell <david-b@pacbell.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>