Rate-limit NetworkStats polls when pulling atoms.

Polling NetworkStats is a heavy operation, and it updates stats
for all networks, so adding a rate-limit avoid unnecessary load.

Perfd workaround is no longer necessary, as perfd does not rely
on network stats atoms anymore.

Test: manual, perfetto, adb shell dumpsys netstats
Bug: 352495181
Flag: com.android.server.stats.apply_network_stats_poll_rate_limit
Change-Id: I113f6067db83570a854de7c2624abfb2e71a8f53