scsi: qla2xxx: edif: Reduce memory usage during low I/O

For edif, each I/O requires a secondary buffer to carry the FCP
cmnd. During high traffic time, these buffers are cached in the qpair. As
traffic dies down, these buffers will be trimmed as needed. If traffic is
reduced to none over 2 consecutive intervals, then these buffers will be
further trimmed.

Free FCP cmnd buffers to reduce memory usage during slow I/O time.

Signed-off-by: Quinn Tran <qutran@marvell.com>
Signed-off-by: Nilesh Javali <njavali@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>