[bgpcfgd] Redistribute static routes

[shi-su]

Why I did it

Enable redistribution of static routes

How I did it

Enable redistribution of static routes when the first route is added to STATIC_ROUTE table of Config_DB and disable the redistribution when the last route is removed from STATIC_ROUTE table.

How to verify it

Check the redistribution is enabled after adding a static route in STATIC_ROUTE table of Config_DB and the route is advertised to other peers

admin@vlab-01:~$ sudo sonic-cfggen -a '{"STATIC_ROUTE":{"default|10.2.0.0/24": {"nexthop": "10.0.0.57"}}}' --write-to-db

vlab-01# show running-config
...
router bgp 65100
...
 address-family ipv4 unicast
  network 10.1.0.32/32
  network 192.168.0.0/21
  redistribute static
...
 address-family ipv6 unicast
  network fc00:1::/64
  network fc02:1000::/64
  redistribute static
...

ARISTA03T1>show ip route 10.2.0.0/24

VRF: default
Codes: C - connected, S - static, K - kernel,
       O - OSPF, IA - OSPF inter area, E1 - OSPF external type 1,
       E2 - OSPF external type 2, N1 - OSPF NSSA external type 1,
       N2 - OSPF NSSA external type2, B - BGP, B I - iBGP, B E - eBGP,
       R - RIP, I L1 - IS-IS level 1, I L2 - IS-IS level 2,
       O3 - OSPFv3, A B - BGP Aggregate, A O - OSPF Summary,
       NG - Nexthop Group Static Route, V - VXLAN Control Service,
       DH - DHCP client installed default route, M - Martian,
       DP - Dynamic Policy Route, L - VRF Leaked

 B E      10.2.0.0/24 [200/0] via 10.0.0.60, Port-Channel1

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012

Description for the changelog

A picture of a cute animal (not mandatory but encouraged)

[lolyu]

hi, @qiluo-msft, could you help confirm if this patch is included in the latest 202012 image, as didn't see this change in 202012.02 image?

[qiluo-msft]

Sorry I made a mistake when labelling. I just cherry-picked it to 202012.

[lolyu]

Sorry I made a mistake when labelling. I just cherry-picked it to 202012.

Thanks @qiluo-msft !