ksmbd: validate :: stream type against directory create

ksmbd: validate :: stream type against directory create

smb2.streams.dir opens <dir>::$DATA with FILE_DIRECTORY_FILE and expects
STATUS_NOT_A_DIRECTORY, then opens <dir>::$DATA without it and expects
STATUS_FILE_IS_A_DIRECTORY.

Commit "treat unnamed DATA stream as base file" canonicalizes the ::$DATA
suffix to a NULL stream name so the open continues through the base-file
path. That skipped the stream/directory type validation, which was
guarded by "if (stream_name)", so opening a directory's ::$DATA stream
with FILE_DIRECTORY_FILE incorrectly returned STATUS_OK and a plain open
of it no longer reported STATUS_FILE_IS_A_DIRECTORY.

parse_stream_name() still records the explicit $DATA type in s_type even
when it clears stream_name.  Run the data-stream vs directory validation
whenever s_type is DATA_STREAM, not only when stream_name is set, so the
canonicalized ::$DATA open is rejected with the correct status.

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