[SCSI] qla4xxx: updated mbx_sys_info struct to sync with FW 4.6.x

Also, changed boundary checking from size of total
structure to verification that we received the amount of
data needed to cache inernally. This change will provide
compatibility with mbx_sys_info structure sizes in both
older and newer firmware versions.

Signed-off-by: Vikas Chaudhary <vikas.chaudhary@qlogic.com>
Signed-off-by: Ravi Anand <ravi.anand@qlogic.com>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>