Multipath load balancing for EBGP and IBGP VPNs

Enables to select EBGP and IBGP paths as candidates for multipath. This can be useful in the context of VPN configurations. This feature is an extension of protocol independent multipath and is configurable only within a routing instance. It can be useful in the context of VPN configurations in which the best path might have been advertised in either EBGP or IBGP.