nbd: move the task_recv check into nbd_size_update

mainline inclusion
from mainline-v5.11-rc1
commit 92f93c3a
category: bugfix
bugzilla: 187706,,https://gitee.com/openeuler/kernel/issues/I5XEBX
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=92f93c3a1bf9dc73181dc6566497d16b690cb576



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nbd_size_update is about to acquire a few more callers, so lift the check
into the function.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Conflicts:
	drivers/block/nbd.c
[0c98057b ("nbd: Fix use-after-free in pid_show") include first]

Signed-off-by: Zhong Jinghua <zhongjinghua@huawei.com>
Reviewed-by: Jason Yan <yanaijie@huawei.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>