zfs_btree_insert_leaf_impl
zfs_btree_insert_leaf_impl(tree, leaf, idx, value);
zfs_btree_insert_leaf_impl(tree, leaf, idx, value);
zfs_btree_insert_leaf_impl(tree, new_leaf, idx - keep_count -
zfs_btree_insert_leaf_impl(tree, new_leaf, 0, buf);