Zombie Pigmen don't path through lava and are too slow

With the new mob AI update, Pigmen will no longer pathfind through lava to get to the player, even though pigmen are immune to lava.

How to replicate:
1. Create a new super flat world in creative and turn mob spawning off (/gamerule doMobSpawning false)
2. Build a lava moat around yourself.
3. Spawn a pigman on the other side
4. go into survival and attack it
5. Pigmen will act slow when trying to attack you, and will also not go into the lava.