bgpd: wire up VPNv6 protocol processing

bgpd: wire up VPNv6 protocol processing

There wasn't much missing for VPNv6 to begin with; just a few bits of
de- & encoding and a few lists to be updated.

Signed-off-by: Lou Berger <lberger@labn.net>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
[Editorial note: Signed-off-by may imply an authorship claim, but need not]

Edited-by: Paul Jakma <paul.jakma@hpe.com> / <paul@jakma.org>
(cherry picked from commit 9da04bca0e994ec92b9242159bf27d89c6743354)

Conflicts:
	bgpd/bgp_attr.c
	bgpd/bgp_mplsvpn.c
	bgpd/bgpd.c