This patch uses the previously introduced TokenBucket to rate limit
ApfProgramEvents, still allowing for burst of ApfProgramEvents when a
new interface is set up (due to ipv4 provisioning, multicast lock, ipv6 RAs
triggering new APF program events in short amounts of time).
Test: new test in IpConnectivityMetricsTest
Bug: 1550402
(cherry picked from commit e3f7299ce2)
Change-Id: Idb640dec13ba64180985544b9709a586af66eb6e
6d442d82d0