only rate limit notification updates

Updates to progress bars are the main culprit in system
performance events caused by apps spamming the notification
service. Rate-limiting only updates allows us to set a lower
threshold wihtout the owrry of mistakenly dropping bursts of
notifications being quickly posted after a network sync.

Also reduce logspam caused by the rate-limit events.

Bug: 30132961
Change-Id: I49acda6a2831204da45e899ddd3d62d571d7174b