bgpd: fix table-map option

[askorichenko]

Schedule zebra to withdraw routes filtered out by a table-map.

[donaldsharp]

can you show me the broken behavior before this change?

[askorichenko]

If a neighbor shares two routes 10.0.0.1/32, 10.10.10.1/32 :

nei# show run
!
router bgp 65002
 bgp router-id 10.255.0.20
 no bgp ebgp-requires-policy
 no bgp network import-check
 neighbor 10.255.0.10 remote-as 65001
 !
 address-family ipv4 unicast
  network 10.0.0.1/32
  network 10.10.10.1/32
 exit-address-family
exit
!

And a peer has a table map to permit only 10.0.0.1/32 route

peer# show run
!
router bgp 65001
 bgp router-id 10.255.0.10
 no bgp ebgp-requires-policy
 neighbor 10.255.0.20 remote-as 65002
 !
 address-family ipv4 unicast
  table-map TableMap
 exit-address-family
exit
!
access-list al seq 5 permit 10.0.0.1/32
!
route-map TableMap permit 10
 match ip address al
exit
!

1. Then the peer STARTS (!) correctly against the above config, and drops (ignores) the filtered out route 10.10.10.1/32

# show ip fib
...
B>* 10.0.0.1/32 [20/0] via 10.255.0.20, ...
C>* 10.255.0.0/24 is directly connected, ...
L>* 10.255.0.10/32 is directly connected, ...

2. Let's remove and then add the table-map option back.
   A removal immediately yields:

peer# no table-map TableMap
...
peer# show ip fib
...
B>* 10.0.0.1/32 [20/0] via 10.255.0.20, ...
B>* 10.10.10.1/32 [20/0] via 10.255.0.20, ... <- a previously missing route was correctly installed
C>* 10.255.0.0/24 is directly connected, ...
L>* 10.255.0.10/32 is directly connected, ...

3. Now set the table-map back and see that this would have NO EFFECT on the fib until we clear the session

peer# table-map TableMap
...
peer# show ip fib
...
B>* 10.0.0.1/32 [20/0] via 10.255.0.20, ...
B>* 10.10.10.1/32 [20/0] via 10.255.0.20, ... <- the route wasn't withdrawn 
C>* 10.255.0.0/24 is directly connected, ...
L>* 10.255.0.10/32 is directly connected, ...

peer# clear bgp *
peer# show ip fib
...
B>* 10.0.0.1/32 [20/0] via 10.255.0.20, ...
C>* 10.255.0.0/24 is directly connected, ...
L>* 10.255.0.10/32 is directly connected, ...

[ton31337]

Please add a topotest for this case because it's seems easy to replicate.

[ton31337]

nit: Can you drop ()?

struct attr local_attr = *pi->attr;

[riw777]

code looks okay ... waiting on topo test