ospf6d: add LSA payload to show summary output

ospf6d: add LSA payload to show summary output

Unlike OSPFv2, the LSID of an LSA isn't sufficient to know what the contents
of the LSA are. Its useful for debugging and basic eyeball tests to see the
contents of the LSA in the simple tabular format of "show ipv6 ospf6 database".
This patch adds that output to the command. It replaces the existing fields of
"duration, Chksum and Length" with a single field called Payload which is
dependent on the LSA type. For Inter-Area Prefix, Intra-Area Prefix and
AS-External LSAs, this will be the advertised prefix/prefix length, for Router
LSAs, it is RtrID/IfID etc.

Signed-off-by: Dinesh G Dutt <ddutt at cumulusnetworks.com>
Reviewed-by: Pradosh Mohapatra <pmohapat at cumulusnetworks.com>
Reviewed-by: Scott Feldman <sfeldma at cumulusnetworks.com>
[DL: rebase fix, line disappeared in ospf6_abr_originate_summary_to_area]
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>