bgpd: instance delete unimport evpn routes

bgpd: instance delete unimport evpn routes

EVPN routes (type-2/type-5) are imported from
default bgp instance (where they are learnt) to
non-default vrf instance.

When a bgp instance (default) is deleted,
unimport evpn routes from vrfs.

In absence of unimport, the imported routes in vrf
has parent path info points to default instance's path
info which is no longer valid (if instance is deleted).
When accessing parent path info leads to a crash
in non-default vrf instance.

The bgp instance is not cleaned up when
'no router bgp ASN' is performed, the instance's
reference count remains for evpn imported routes.

Ticket:CM-24484
Reviewed By:

Testing Done:
Validated via learning EVPN type-2/type-5 routes in symmetric
routing scenario.
The routes are imported to VRFs based on corresponding
L3VNI. When the default instance is removed, the evpn routes
are cleaned up from the VRF instance.

TURTLE(config)# do show bgp vrf vrf3 ipv4 unicast

   Network          Next Hop            Metric LocPrf Weight Path
*> 70.1.0.0/16      0.0.0.0                            32768 i
s  70.1.1.24/32     110.0.0.2                              0 65100 65002 i
s>                  110.0.0.2                              0 65100 65002 i
s  70.1.1.43/32     110.0.0.4                              0 65100 65004 i
s>                  110.0.0.4                              0 65100 65004 i

TURTLE(config)# no router bgp 65050
TURTLE(config)# do show bgp vrf vrf3 ipv4 unicast
No BGP prefixes displayed, 0 exist

Signed-off-by: Chirag Shah <chirag@cumulusnetworks.com>