Relocation COWs metadata blocks in two cases for the reloc root:

- copying the subvolume root item when creating the reloc root
- copying a btree node when there is a COW during relocation

In both cases, the resulting btree node hits an abnormal code path with
respect to the owner field in its btrfs_header. It first creates the
root item for the new objectid, which populates the reloc root id, and
it at this point that delayed refs are created.

Later, it fully copies the old node into the new node (including the
original owner field) which overwrites it. This results in a simple
quotas mismatch where we run the delayed ref for the reloc root which
has no simple quota effect (reloc root is not an fstree) but when we
ultimately delete the node, the owner is the real original fstree and we
do free the space.

To work around this without tampering with the behavior of relocation,
add a parameter to btrfs_add_tree_block that lets the relocation code
path specify a different owning root than the "operating" root (in this
case, owning root is the real root and the operating root is the reloc
root). These can naturally be plumbed into delayed refs that have the
same concept.

Note that this is a double count in some sense, but a relatively natural
one, as there are really two extents, and the old one will be deleted
soon. This is consistent with how data relocation extents are accounted
by simple quotas.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>