OAM support with LDP IPv6

MPLS OAM tools lsp-ping and lsp-trace are updated to operate with LDP IPv6 and support the following:

The behavior at the sender and receiver nodes is updated to support both LDP IPv4 and IPv6 target FEC stack TLVs. Specifically:

Finally, vccv-ping and vccv-trace for a single-hop PW are updated to support IPv6 PW FEC 128 and FEC 129 as per RFC 6829. In addition, the PW OAM control word is supported with VCCV packets when the control-word option is enabled on the spoke-SDP configuration. The value of the Channel Type field is set to 0x57, which indicates that the Associated Channel carries an IPv6 packet, as per RFC 4385.