[Multi-asic][20191130] The default route in APP_DB is not removed after bgp shutdown

[arlakshm]

Description

Steps to reproduce the issue:

1.Load latest 20191130 image and bring-up the sonic-mgmt topology t1-64-lag
2. Start all ebgp sessions and verify the default route is learnt.
3.Shutdown ebgp sessions and check the default route is removed in the control plane and APP_DB

Describe the results you received:

After shutdown eBGP sessions the default route is still present in the APP_DB.

Logs:

When all eBGP sessions are up

admin@sonic:~$ show ip route 0.0.0.0/0
Routing entry for 0.0.0.0/0
  Known via "kernel", distance 210, metric 0
  Last update 00:22:26 ago
  * 240.127.1.1, via eth0

Routing entry for 0.0.0.0/0
  Known via "bgp", distance 20, metric 0, best
  Last update 00:15:32 ago
  * 10.0.0.5, via PortChannel105
  * 10.0.0.1, via PortChannel102
  * 10.0.0.9, via PortChannel108
  * 10.0.0.13, via PortChannel1011

admin@sonic:~$ sonic-db-cli -n asic0 APPL_DB hgetall "ROUTE_TABLE:0.0.0.0/0"
nexthop
10.0.0.1,10.0.0.5
ifname
PortChannel102,PortChannel105

The nexthops are Portchannel connecting eBGP peers

When all eBGP sessions are shutdown
The route is removed from control plane

admin@sonic:~$ show ip route 0.0.0.0/0
Routing entry for 0.0.0.0/0
  Known via "kernel", distance 210, metric 0, best
  Last update 00:22:47 ago
  * 240.127.1.1, via eth0

admin@sonic:~$ sonic-db-cli -n asic0 APPL_DB hgetall "ROUTE_TABLE:0.0.0.0/0"
nexthop
10.1.0.0
ifname
PortChannel44

PortChannel44 is link connecting backend ASIC

Describe the results you expected:

default route should be removed

Output of show version:

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Output of show techsupport:

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Additional information you deem important (e.g. issue happens only occasionally):