ksmbd: fix translation in smb2_populate_readdir_entry()

When transferring ownership information to the
client the k*ids are translated into raw *ids before they are sent over
the wire. The function currently erroneously translates the k*ids
according to the mount's idmapping. Instead, reporting the owning *ids
to userspace the underlying k*ids need to be mapped up in the caller's
user namespace. This is how stat() works.
The caller in this instance is ksmbd itself and ksmbd always runs in the
initial user namespace. Translate according to that.

The idmapping of the mount is already taken into account by the lower
filesystem and so kstat->*id will contain the mapped k*ids.

Switch to from_k*id_munged() which ensures that the overflow*id is
returned instead of the (*id_t)-1 when the k*id can't be translated.

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>