bgpd: fix bgp node created at withdraw event

The prefixes unexportation triggers an attempt to create
the VPN prefix node if that prefix was not already present.

For instance, if a given prefix is not exported because of
a route-map filtering, the withdraw process will try to
create the node with the 'bgp_afi_node_get()' command.

Fix this by replacing this call by the 'bgp_safi_node_lookup()'
function.

Fixes: ddb5b48 ("bgpd: vpn-vrf route leaking")
Signed-off-by: Philippe Guibert <[email protected]>

bgpd/bgp_mplsvpn.c

@@ -1903,14 +1903,14 @@ void vpn_leak_from_vrf_withdraw(struct bgp *to_bgp,		/* to */
 		return;
 	}
 
-	if (debug)
-		zlog_debug("%s: withdrawing (path_vrf=%p)", __func__, path_vrf);
-
-	bn = bgp_afi_node_get(to_bgp->rib[afi][safi], afi, safi, p,
-			      &(from_bgp->vpn_policy[afi].tovpn_rd));
+	bn = bgp_safi_node_lookup(to_bgp->rib[afi][safi], safi, p,
+				  &(from_bgp->vpn_policy[afi].tovpn_rd));
 
 	if (!bn)
 		return;
+	if (debug)
+		zlog_debug("%s: withdrawing (path_vrf=%p)", __func__, path_vrf);
+
 	/*
 	 * vrf -> vpn
 	 * match original bpi imported from