debian: enable xfs_scrub_all systemd timer services by default

debian: enable xfs_scrub_all systemd timer services by default

Now that we're finished building online fsck, enable the periodic
background scrub service by default.  This involves the postinst script
starting the resource management slice and the timer.

No other sub-services need to be enabled or unmasked explicitly.  They
also shouldn't be started or restarted because that might interrupt
background operation unnecessarily.

Although the xfs_scrub_all timer is activated by default, the individual
xfs_scrub@ services that it spawns will only do real work on filesystems
that are new enough to have back reference metadata available.  This
avoids surprises for people who are upgrading Debian; only new installs
with new mkfs will get any automatic fsck behavior.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>