LU-15827 osd: respect filldir buffer limits

LU-15827 osd: respect filldir buffer limits

In osd_ldiskfs_filldir() ensure that the encoded name also fits in the
buffer. In osd_ldiskfs_filldir() and obj_name2lu_name() remove a
superfluous and potentially incorrect check on names that appear to be
FIDs.

Lustre-change: https://review.whamcloud.com/47224
Lustre-commit: 5879647624c834d4a579f425a0fc8d408235e275

Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: I1540f058801b002474ceac1206317344cebb1084
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-on: https://review.whamcloud.com/47325
Tested-by: jenkins <devops@whamcloud.com>