The exit arcs of IPv4 and IPv6 are not identical, yet the vnet classifier assumes they are identical.

The following CLI commands fail an assertion when selecting the next node.

classify table mask l3 ip4 proto table 0
ip route add 224.0.0.0/24 via classify 0
classify session hit-next node tap-inject-classified table-index 0 match l3 ip4 proto 89

Here tap-inject-classified is a node defined in a plugin.
The same failure is produced with other nodes, e.g. error-drop.

It is not enough to simply remove the ASSERT() as the fundamental assumption that the ip4 and ip6 arcs are the same is not true. The unformat_ip_next_node() scheme needs to be re-thought to allow possibly different ip4-classify and ip6-classify next_nodes.