gfs2: Automatically set GFS2_DIF_SYSTEM flag on system files

When new files and directories are created inside a parent directory
we automatically inherit the GFS2_DIF_SYSTEM flag (if set) and assign
it to the new file/dirs.

All new system files/dirs created in the metafs by, say gfs2_jadd,
will have this flag set because they will have parent directories in
the metafs whose GFS2_DIF_SYSTEM flag has already been set (most likely
by a previous mkfs.gfs2)

Signed-off-by: Abhi Das <adas@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>