The sid_to_id() helper encodes raw ownership information suitable for
s*id handling. This is conceptually equivalent to reporting ownership
information via stat to userspace. In this case the consumer is ksmbd
instead of a regular user. So when encoding raw ownership information
suitable for s*id handling later we need to map the id up according to
the user namespace of ksmbd itself taking any idmapped mounts into
account.

Cc: Steve French <stfrench@microsoft.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Namjae Jeon <namjae.jeon@samsung.com>
Cc: Hyunchul Lee <hyc.lee@gmail.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: linux-cifs@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>