[PATCH] sbp2: default to serialize_io=1

Set serialize_io=1 by default.  This is safer and required by seemingly more
and more hardware.  It causes little or no performance loss for S400 devices.
Performance of S800 1394b devices may drop by 25...30%.  Therefore make the
parameter's description and dmesg message clearer about performance impact.

Update description of the max_speed parameter too.  IEEE1394_SPEED_MAX is
currently S800.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Jody McIntyre <scjody@steamballoon.com>
Cc: Ben Collins <bcollins@debian.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>