ksmbd: validate mech token in session setup

commit 92e47016 upstream.

If client send invalid mech token in session setup request, ksmbd
validate and make the error if it is invalid.

Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-22890
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>