xfs_repair: check free rt extent count

Check the superblock's free rt extent count against what we observed.
This increases the runtime and memory usage, but we can now report
undercounting frextents as a result of a logging bug in the kernel.
Note that repair has always fixed the undercount, but it no longer does
that silently.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Chandan Babu R <chandan.babu@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
4 files changed