- Add methods to start and stop IPv6 forwarding upstream - Populate the upstream IPv6 map when the first rule for any upstream/downstream pair is created. - Clear the upstream IPv6 map when the last rule for any upstream/downstream pair is deleted. Test: Added coverage to IpServerTest and BpfCoordinatorTest Change-Id: Ib041081e95f5f449489ab63138de034222ffac8f