Attribute "generic.attack_knockback" doesn't work for iron golems

When I summoned an iron golem with the attribute "generic.attack_knockback", it still dealt the same knockback.

To Reproduce:

1. /summon iron_golem ~ ~ ~ {Attributes:[{Name:"generic.attack_knockback",Base:10}]}

2. Spawn a hostile mob.

3. Notice the lack of change in the iron golem's knockback distance.