xfs_repair: slab and bag structs need to track more than 2^32 items

xfs_repair: slab and bag structs need to track more than 2^32 items

Currently, the xfs_slab data structure in xfs_repair is used to stage
incore reverse mapping and reference count records to build the ondisk
rmapbt and refcountbt during phase 5.

On a reflink filesystem, it's possible for there to be more than 2^32
forward mappings in an AG, which means that there could be more than
2^32 rmapbt records too.  Widen the size_t fields of xfs_slab to u64
accomodate this.

Similarly, the xfs_bag structure holds pointers to xfs_slab objects.
This abstraction tracks rmapbt records as we walk through the AG space
building refcount records.  It's possible for there to be more than 2^32
mappings to a piece of physical space, so we need to side the size_t
fields of xfs_bag to u64 as well.

In the next patch we'll fix all the users of these two structures; this
is merely the preparatory patch.

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