docs: Document what address-family ipv4 unicast import vrf route-map <ROUTE-MAP> does

[robinchrist]

It is possible to configure the following:

router bgp AS
 address-family ipv4 unicast
  import vrf route-map foobar
  import vrf myVRF
 exit-address-family

The import vrf route-map foobar doesn't appear to be documented.

I assume this filters all the routes that are imported (one common filter for all VRFs)? Is this correct?

I tested with the following test case:

If I configure

VRF default:
B>* 10.255.11.0/24 [20/0] is directly connected, myVRF (vrf myVRF), weight 1, 00:00:17
B>* 10.255.12.0/24 [20/0] is directly connected, myVRF (vrf myVRF), weight 1, 00:00:17
B>* 10.255.13.0/24 [20/0] is directly connected, myVRF (vrf myVRF), weight 1, 00:00:17

VRF myVRF:
C>* 10.255.11.0/24 is directly connected, br1.1001, weight 1, 22:34:23
K * 10.255.11.0/24 [0/0] is directly connected, br1.1001, weight 1, 23:07:26
C>* 10.255.12.0/24 is directly connected, br1.1002, weight 1, 22:34:23
K * 10.255.12.0/24 [0/0] is directly connected, br1.1002, weight 1, 23:07:13
C>* 10.255.13.0/24 is directly connected, br1.1003, weight 1, 22:34:23
K * 10.255.13.0/24 [0/0] is directly connected, br1.1003, weight 1, 23:07:13

Now configure additionally:

ip prefix-list TEST_PREFIXES_TO_LEAK seq 10 permit 10.255.11.0/24

route-map TestMap1 permit 10
 match ip address prefix-list TEST_PREFIXES_TO_LEAK
exit

router bgp AS
 address-family ipv4 unicast
  import vrf route-map TestMap1
  import vrf myVRF
 exit-address-family

You will now see:

VRF default:
B>* 10.255.11.0/24 [20/0] is directly connected, myVRF (vrf myVRF), weight 1, 00:00:17

VRF myVRF:
C>* 10.255.11.0/24 is directly connected, br1.1001, weight 1, 22:34:23
K * 10.255.11.0/24 [0/0] is directly connected, br1.1001, weight 1, 23:07:26
C>* 10.255.12.0/24 is directly connected, br1.1002, weight 1, 22:34:23
K * 10.255.12.0/24 [0/0] is directly connected, br1.1002, weight 1, 23:07:13
C>* 10.255.13.0/24 is directly connected, br1.1003, weight 1, 22:34:23
K * 10.255.13.0/24 [0/0] is directly connected, br1.1003, weight 1, 23:07:13