zfs_refcount_transfer
zfs_refcount_transfer(&nhdr->b_l1hdr.b_refcnt, &hdr->b_l1hdr.b_refcnt);
zfs_refcount_transfer(&ndn->dn_holds, &odn->dn_holds);
void zfs_refcount_transfer(zfs_refcount_t *, zfs_refcount_t *);