IpManager: use InitialConfiguration for provisioning

This patch changes IpManager to take into account static provisioning
information specified in the InitialConfiguration for IPv6 static
configuration.

When a valid InitialConfiguration with IPv6 content is specified,
IpManager will do the following things:

- at start(), it will push the IPv6 addresses in the config to netd
- it will observe all addresses be notified via Netlink
- when all addresses are there, it will patch in the associated IPv6
  routes in the config, so that they get passed to ConnectivityService
  through the usual mechanism

The logic triggering onProvisioningSuccess is also changed to take into
account InitialConfiguration: when all addresses and all routes in the
config are seen the provisioning is successful.

Bug: 62988545
Test: runtest frameworks-net, with newly added tests
Change-Id: I77ed7c576c4b198de7a4726be70c78b74689e98b