xfs_scrub: hoist repair retry loop to repair_item_class

xfs_scrub: hoist repair retry loop to repair_item_class

For metadata repair calls, move the ioctl retry and freeze permission
tracking into scrub_item.  This enables us to move the repair retry loop
out of xfs_repair_metadata and into its caller to remove a long
backwards jump, and gets us closer to vectorizing scrub calls.

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