ls: make -Z output compatible with GNU coreutils 8.25

ls: make -Z output compatible with GNU coreutils 8.25

This also makes it clear that LIST_MODEBITS == LIST_LOPT

function                                             old     new   delta
ls_main                                              752     777     +25
display_files                                        400     399      -1
display_single                                      1055    1053      -2
my_stat                                              320     317      -3
packed_usage                                       32311   32280     -31
.rodata                                           168895  168864     -31
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/5 up/down: 25/-68)            Total: -43 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>