zebra: Refine cleanup when a VRF with configuration gets deleted

zebra: Refine cleanup when a VRF with configuration gets deleted

When a VRF gets deleted - e.g., networking restart or ifdown of the VRF - but
has associated FRR configuration, additional cleanup of all dynamic data pertaining
to this VRF is necessary. This includes the routing tables, next hop tables,
temporary queues for this VRF etc. Only the FRR configuration for this VRF must
be retained.

Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>
Reviewed-by:   Don Slice <dslice@cumulusnetworks.com>
Reviewed-by:   Mitesh Kanjariya <mitesh@cumulusnetworks.com>
Reviewed-by:   Donald Sharp <sharpd@cumulusnetworks.com>
Ticket: CM-19148
Reviewed By: CCR-7030
Testing Done:
1. Manual testing - This scenario and EVPN configuration
2. Various smoke tests - vrf, bgp, pim, l3-smoke