LU-3232 build: Move fsfilt_ldiskfs.ko into lustre-osd-ldiskfs

The fsfilt_ldiskfs.ko module depends on symbols in osd_ldiskfs.ko and
ldiskfs.  However, osd_ldiskfs.ko is only part of the optional package
lustre-osd-ldiskfs, while fsfilt-ldiskfs.ko is in the non-optional
package lustre-modules.

This means that a person using only the lustre-osd-zfs osd will see a
screen full of warnings about missing ldiskfs-related symbols.

We remedy this problem by moving the fsfilt-ldiskfs.ko into the
lustre-osd-ldiskfs rpm.

Change-Id: I631a98dd56c7d4df69266e4f922f949132774d84
Signed-off-by: Christopher J. Morrone <morrone2@llnl.gov>