CTS for ingress rate limiting

This test creates a TUN interface and registers it with
ConnectivityService. For 15 seconds, it continuously writes data to that
interface and measures at what rate it is received.

Data accounting is currently not covered by this test.

Test: atest RateLimitTest
Bug: 172053704
Change-Id: I74f891f3b7113855375c48a10cefbfe47221931b
1 file changed