LU-14734 ldiskfs: improve message for large_dir

LU-14734 ldiskfs: improve message for large_dir

Make it more clear that the large_dir feature has already been
enabled, rather than making the admin think that they need to
enable the feature themselves.

Lustre-change: https://review.whamcloud.com/45046
Lustre-commit: 2a24b6ec67da9224e1cb6226166cde3a9c95431d

Test-Parameters: trivial
Fixes: f5967b06aac5 ("LU-14734 osd-ldiskfs: enable large_dir automatically")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ica59d3370148ed277d3541c05be065c4638daf8d
Reviewed-on: https://review.whamcloud.com/46045
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>