Zebra: Fix VRF-id and table for BGP unnumbered (RFC 5549)

Zebra: Fix VRF-id and table for BGP unnumbered (RFC 5549)

In the case of BGP unnumbered RFC 5549 (IPv4 routes with IPv6 nexthop), the
zebra code to handle routes was not initializing the correct VRF id and
locating the correct routing table, resulting in the routes not getting
installed. Fixed with this change.

Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>
Reviewed-by:   Donald Sharp <sharpd@cumulusnetworks.com>
Ticket: CM-10247
Reviewed By: CCR-4429
Testing Done: Manual verification