ksmbd: Reduce error log 'speed is unknown' to debug

mainline inclusion
from mainline-5.15-rc1
commit d475866e
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I60T7G
CVE: NA

Reference: https://git.kernel.org/torvalds/linux/c/d475866eeed8



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This log happens on servers with a network bridge since
the bridge does not have a specified link speed.
This is not a real error so change the error log to debug instead.

Signed-off-by: Per Forlin <perfn@axis.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>