Walls from before 1.16 don't have the correct block states when upgrading worlds to modern versions

When you build walls on top of and besides each other in 1.15, they all get the <direction>=true state, in 1.16, the top layer gets <direction>=short and the lower layers get <direction>=tall, this is correct.

But when upgrading from 1.15 to new versions, the context of the direction states isn't correctly checked, and just maps false=none and true=short. A block update will correct the walls.