xfs: force small EFIs for reaping btree extents

xfs: force small EFIs for reaping btree extents

Source kernel commit: 3f3cec031099c37513727efc978a12b6346e326d

Introduce the concept of a defer ops barrier to separate consecutively
queued pending work items of the same type.  With a barrier in place,
the two work items will be tracked separately, and receive separate log
intent items.  The goal here is to prevent reaping of old metadata
blocks from creating unnecessarily huge EFIs that could then run the
risk of overflowing the scrub transaction.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bill O'Donnell <bodonnel@redhat.com>