zebra: GR code could potentially stop running

zebra: GR code could potentially stop running

When GR is running and attempting to clear up a node
if the node that is currently saved and we are coming
back to happens to be deleted during the time zebra
suspends the GR code due to hitting the node limit
then zebra GR code will just completely stop processing
and potentially leave stale nodes around forever.

Let's just remove this hole and process what we can.
Can you imagine trying to debug this after the fact?

If we remove a node then that counts toward the maximum
to process of ZEBRA_MAX_STALE_ROUTE_COUNT.  This should
prevent any non-processing with a slightly larger cost
of having to look at a few nodes repeatedly

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