ksmbd returned "Input/output error" when mounting with vers=2.0 to
ksmbd. It should return STATUS_NOT_SUPPORTED on unsupported smb2.0
dialect.

Cc: stable@vger.kernel.org
Reported-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>