This is preparation for tetherOffloadRule4Clear test.
- Upstream interface can be set {null, cellular (rawip), wifi (ether)}
- Allow that add up to two downstream interfaces which has one client
on each of them.
- Change mBpfDownstream4Map and mBpfUpstream4Map from mocked instance
to TestBpfMap for further rule check.
- Remove startPolling() from initBpfCoordinatorForRule4() because
upstream information is updated by updateUpstreamNetworkState now.
Test: atest TetheringCoverageTests
Change-Id: Ibc1f68131410b7cec379ab4e310b90ad85f25d31
154b1e467d