blk-mq: fix kabi broken due to request_wrapper

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I65K8D


CVE: NA

--------------------------------

Before commit f60df4a0 ("blk-mq: fix kabi broken in struct
request"), drivers will got cmd address right after request, however,
after this commit, drivers will got cmd address after request_wrapper
instead, which is bigger than request and will cause compatibility
issues.

Fix the problem by placing request_wrapper behind cmd, so that the
cmd address for drivers will stay the same.

Before commit:		|request|cmd|
After commit:		|request|request_wrapper|cmd|
With this patch:	|request|cmd|request_wrapper|

Performance test: arm64 Kunpeng-920 96 core

1) null_blk setup:
modprobe null_blk nr_devices=0 &&
    udevadm settle &&
    cd /sys/kernel/config/nullb &&
    mkdir nullb0 &&
    cd nullb0 &&
    echo 0 > completion_nsec &&
    echo 512 > blocksize &&
    echo 0 > home_node &&
    echo 0 > irqmode &&
    echo 1024 > size &&
    echo 0 > memory_backed &&
    echo 2 > queue_mode &&
	echo 4096 > hw_queue_depth &&
	echo 96 > submit_queues &&
    echo 1 > power

2) fio test script:
[global]
ioengine=libaio
direct=1
numjobs=96
iodepth=32
bs=4k
rw=randwrite
allow_mounted_write=0
time_based
runtime=60
group_reporting=1
ioscheduler=none
cpus_allowed_policy=split
cpus_allowed=0-95

[test]
filename=/dev/nullb0

3) iops test result:

without this patch:	23.9M
with this patch:	24.1M

Fixes: f60df4a0 ("blk-mq: fix kabi broken in struct request")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>