scsi: qla2xxx: Performance tweak

Move statistics fields from vha struct to qpair to reduce memory thrashing.

Link: https://lore.kernel.org/r/20200904045128.23631-8-njavali@marvell.com
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
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>