[SCSI] aacraid: 17 element sg performance update

Received From Mark Salyzyn.

The Jaguar and Corsair class of adapters (2410, 2810, 2610, 21610, CERC)
perform better (about 10% better read performance, write performance
neutral) with current Firmware if the OS limits the number of scatter
gather elements to 17 per request.

Signed-off-by: Mark Haverkamp <markh@osdl.org>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>