* Introduced new cmdline flag --bgp-port, which controls BGP Server listening port and remote port of in-cluster node peers
* Introduced new cmdline flag --peer-router-ports, which controls remote BGP port for external peers
* Introduced new node annotation kube-router.io/peer.ports with same effect as --peer-router-ports
* Introduces the option --override-nexthop, setting it to true will make
advertised next hop for the routers to the peers will be automatically
selected to be appropriate reachable local IP. This will be overrider
any next-hop set for the routes in the RIB. Kube-router by defauly set
the next-hop to `node IP` which is not correct in case of nodes with
multiple interfaces and use differnt interaces for differect external
peers.
Fixes#480
* add next-hop-self documentation
* Node should advertise its pod CIDR to external BGP peers only if
--advertise-node-pod-cidr is set to true (defaults to true).
This is to enable a case where pod's remain non-routable from out of the
cluster but service VIP's can be routable from out side the cluster.
* fix unit test
* address review comments
