ksmbd: remove smb2_buf_length in smb2_transform_hdr

mainline inclusion
from mainline-5.16-rc1
commit 2dd9129f
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I60T7G
CVE: NA

Reference: https://git.kernel.org/torvalds/linux/c/2dd9129f7dec



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To move smb2_transform_hdr to smbfs_common, This patch remove
smb2_buf_length variable in smb2_transform_hdr.

Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Zhong Jinghua <zhongjinghua@huawei.com>