nbd: refactor size updates

mainline inclusion
from mainline-v5.11-rc1
commit 2dc691cc
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=2dc691cc4ac259f8b5bb0bd8670645af894d30eb



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Merge nbd_size_set and nbd_size_update into a single function that also
updates the nbd_config fields.  This new function takes the device size
in bytes as the first argument, and the blocksize as the second argument,
simplifying the calculations required in most callers.

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

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>