maple_tree: Fix spanning_rebalance() insufficient nodes and mas state.

maple_tree: Fix spanning_rebalance() insufficient nodes and mas state.

Fix mas state when expanding a root, the offset on rebalance, and the node and offset
when doing a spanning store.

Note that spanning rebalance needed to do some tricky free/no free based on
where the node data comes from.  Next would skip the free of the next node
as it is picked up when mas_topiary() trims the parents children

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>