IPv6 support for static egress LSPs

Static LSPs on the egress router can be configured with IPv6 as the next-hop address for forwarding IPv6 traffic. Previously, only IPv4 static LSPs were supported. The IPv6 static LSPs share the same transit, bypass, and static LSP features of IPv4 static LSPs. A commit failure occurs when the next-hop address and destination address of the static LSP do not belong to the same address family (IPv4 or IPv6).