SRv6 support

[brmcdoug]

BGP-LS supports collection and export of SRv6 data.
https://datatracker.ietf.org/doc/draft-dawra-idr-bgpls-srv6-ext/

Because OpenBMP supports ingest of BGP-LS IPv4, IPv6, and segment routing data, it should also support SRv6 link state and SID information.