USB: serial: introduce a flag into the usb serial layer to tell drivers that their URBs are killed due to suspension

This patch introduces a flag into the usb serial layer to tell drivers
that their URBs are killed due to suspension. That is necessary to let
drivers know whether they should report an error back.
Signed-off-by: NOliver Neukum <oneukum@suse.de>

Hi Greg,

this is for 2.6.30. Patches to use this in drivers are under development.

	Regards
		Oliver