scsi: qla2xxx: Fix a race condition between aborting and completing a SCSI command

Instead of allocating a struct srb dynamically from inside .queuecommand(),
set qla2xxx_driver_template.cmd_size such that struct scsi_cmnd and struct
srb are contiguous. Do not call QLA_QPAIR_MARK_BUSY() /
QLA_QPAIR_MARK_NOT_BUSY() for SRBs associated with SCSI commands. That is
safe because scsi_remove_host() is called before queue pairs are deleted
and scsi_remove_host() waits for all outstanding SCSI commands to finish.

Cc: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Himanshu Madhani <hmadhani@marvell.com>
Reviewed-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>