Adds ingress rate limiting functionality to ConnectivityService. The tc
rate limit is installed before we tell netd about the interface, and
removed after the network is removed from netd. When the setting
changes, the old rate limit needs to be removed before a new one can be
added (unfortunately, we cannot use NLM_F_REPLACE when configuring the
tc-police filter).

Currently, this functionality is always enabled, but may or may not work
based on kernel support.

Bug: 157552970
Test: atest FrameworksNetTests:ConnectivityServiceTest
Change-Id: I4e64b2c40490f061e42b40a1b1b3a6618c3d1a87