Controller ipv6 support

Changes in src/net, src/bgp, src/control-node, src/schema, src/base
* bgp-peering
* xmpp-peer support
* ipv6/ipv6-vpn table/route support
* mobility for ipv6
* other infra to make it work
* unit-tests for the code including tests indicated by code-coverage

Change-Id: I5727af61cc7b6eee657c710c78198082b2db2f0f