[c-nsp] route-target import on non-leaking PEs

[Alberto Tonso]

I would just add the RTs from all customers to the default-route of the
service VRF on all the PEs exporting it. This way you only need to take
care of the route-leaking on the routers serving the default-route and all
is centrally controlled. If you do mistake then no PE will see the default,
if done right all PEs will see it. But if you control import and export of
the service RTs also on all customer PEs you could always run in just
partially working setup (mismatchs of RTs on one PE and not the other).

The problem with the RDs and multi-path and backup routes can also be
solved on RRs themselves, peering with RR1 prefers PE1 and RR2 prefers PE2.

regards