Adjust animal stances.

There have been complaints on the forums (e.g. https://wildfiregames.com/forum/topic/51245-how-do-you-guys-feel-about-a25-in-terms-of-how-much-fun-you-have-compared-to-a23-or-a24/#comment-446690).
Boar and walrus now behave the same as the elephants (only attack back when attacked), whilst most other animals have defensive stance (attack only within some smaller distance and chase until left vision).

Differential revision: https://code.wildfiregames.com/D4533
Reviewed by: @marder, @wowgetoffyourcellphone
Comment by: @Silier