[SCSI] qla4xxx: Remove hiwat code so scsi eh does not get escalated when we can make progress

Removed unnecessary hiwat code to free up the number available IOCBs.
Eliminates unnecessary eh_ escalations due to inability to obtain IOCB
pkt for marker.

v2.
- Remove define not used anymore and fix req_q_coun accounting.

Signed-off-by: Karen Higgins <karen.higgins@qlogic.com>
[michaelc: ported patch from qlogic.com driver to upstream]
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>