ksmbd: reduce smb direct max read/write size

mainline inclusion
from mainline-5.17-rc4
commit deae24b0
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I60T7G
CVE: NA

Reference: https://git.kernel.org/torvalds/linux/c/deae24b0b13f



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ksmbd does not support more than one Buffer Descriptor V1 element in
an smbdirect protocol request. Reducing the maximum read/write size to
about 512KB allows interoperability with Windows over a wider variety
of RDMA NICs, as an interim workaround.

Reviewed-by: Tom Talpey <tom@talpey.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>