xfsprogs: duplicate extent btrees in xfs_repair need locking

xfsprogs: duplicate extent btrees in xfs_repair need locking

The per-ag duplicate extent btrees can be search concurrently from multiple
threads. This occurs when inode extent lists are being processed and inodes
with extents in the same AG are checked concurrently. The btrees have an
internal traversal cursor, so doing concurrent searches can result in the
cursor being corrupted for both searches.

Add an external lock for each duplicate extent tree and use it for searches,
inserts and deletes to ensure that we don't trash the state of any operation.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>