xfs: hook live realtime rmap operations during a repair operation

Hook the regular realtime rmap code when an rtrmapbt repair operation is
running so that we can unlock the AGF buffer to scan the filesystem and
keep the in-memory btree up to date during the scan.

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