bgpd: Prevent vrf 2 vrf route leaking from going offbox.

bgpd: Prevent vrf 2 vrf route leaking from going offbox.

The vrf 2 vrf route leaking auto-derives RD and RT and
installs the routes into the appropriate vpn table.
These routes when a operator configured ipv[4|6] vpn
neighbors were showing up off box.  The RD and RT
values choosen are localy significant but globaly
useless and may cause confusion.

Put a special bit of code in to notice that we
should not be advertising these routes off box.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>