LDP IPv6 control and data planes

SRĀ OS extends the LDP control plane and data plane to support LDP IPv6 adjacency and session using 128-bit LSR-ID.

The implementation allows for concurrent support of independent LDP IPv4 (32-bit LSR-ID) and IPv6 (128-bit LSR-ID) adjacencies and sessions between peer LSRs and over the same or different set of interfaces.