Check AAE throttle only when AAE is enabled

Move the AAE throttle check to the actual tick function to prevent it
from running when AAE is disabled.  Otherwise, users see AAE throttle
messages when AAE is not enabled and that is just plain confusing.
Merge pull request #1004 from basho/bugfix/969

Check AAE throttle only when AAE is enabled

Reviewed-by: slfritchie