usb-storage: use max_hw_sectors instead of max_sectors

usb-storage: use max_hw_sectors instead of max_sectors

This patch (as1347) makes some adjustments to the way usb-storage
handles the request-queue parameters.

USB host controllers are able to handle arbitrarily long
scatter-gather lists, since they are limited only by main memory and
not by the controller hardware.  Hence the sg_tablesize field in the
host template can be increased to the maximum value.

Drivers like usb-storage aren't supposed to touch the queue's
max_sectors parameter; instead they are supposed to use the
max_hw_sectors value.  Accordingly, the patch replaces calls of
queue_max_sectors() with calls of queue_max_hw_sectors().  Oddly
enough, the blk_queue_max_sectors() routine is nevertheless still
appropriate.

The existing code imposes a limit of SCSI_DEFAULT_MAX_SECTORS (1024)
on the values accepted by the max_sectors attribute file.  There's no
reason not to accept larger values, so the limit is removed.  (It
would be nice to change the file's name to max_hw_sectors, but the old
name is already a well-established API.)

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Matthew Dharm <mdharm-usb@one-eyed-alien.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>