When the third policy gets added, the kernel must replace the nodes for
the 10.0.0.0/24 and 10.0.0.1/24 policies with a single one and must merge
all the subtrees/lists stored in those nodes into the new node.
The existing test cases only have overlaps with a single node, so no
merging takes place (we can always remove the 'old' node and replace
it with the new subnet prefix).
Add a few 'block policies' in a pattern that triggers this, with a priority
that will make kernel prefer the 'esp' rules.
Make sure the 'tunnel ping' tests still pass after they have been added.