Zebra: Fix static NHT for multiple routes scenario

Zebra: Fix static NHT for multiple routes scenario

Ticket: CM-7482
Reviewed By: CCR-3518
Testing Done: Manual verification (on 2.5-br)

When a static route has a nexthop change but the route is also learnt
through another protocol, ensure that the nexthop tracking code marks
the correct route entry (RIB) for processing.

This is a port of patch zebra-static-nht-fixes2.patch from 2.5-br.

Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>
Reviewed-by:   Donald Sharp <sharpd@cumulusnetworks.com>
Reviewed-by:   Dinesh Dutt <ddutt@cumulusnetworks.com>