Use INVALID_UID and INVALID_GID instead of NO_CHANGE_64 to indicate
the value should not be changed.

In cifs_fill_unix_set_info convert from kuids and kgids into uids and
gids that will fit in FILE_UNIX_BASIC_INFO.

Cc: Steve French <smfrench@gmail.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>