bgpd: bugfix vpn->vrf leak: unicast-originated routes are local non-LSP

bgpd: bugfix vpn->vrf leak: unicast-originated routes are local non-LSP

In general, routes leaked from the vpn rib to a vrf include any
labels that might have been attached to the vpn route. VRF routes
that have labels attached require a label-switched path and therefore
require nexthops with labels in order to be marked valid by the
nexthop-tracking logic.

However, some routes in the vpn RIB originated in vrfs local to this
router. Even though they may have labels, we must omit the labels
when leaking to a vrf because traffic using those resulting routes
will be carried by this router via IP routing and not label switching.
The nexthops of these routes do not need to indicate a label-switched
path, and thus the routes should be marked valid even when their nexthops
do not have labels.

This changeset omits labels from vpn->vrf leaked routes when the ultimate
source of the vpn route was a local vrf.

Signed-off-by: G. Paul Ziemba <paulz@labn.net>