[BOT.5] Move class Ipv6ForwardingRule from IpServer to the coordinator

This is a preparation for moving adding/removing forwarding rules from
IpServer to BpfCoordinator.

Bug: 150736748
Test: atest IpServerTest
Original-Change: https://android-review.googlesource.com/1317234
Merged-In: I85316ef09ff3c9389ded11dcc384493d699da48e
Change-Id: I85316ef09ff3c9389ded11dcc384493d699da48e
2 files changed