bgpd: fix label in adj-rib-out

After modifying the "label vpn export value", the vpn label information
of the VRF is not updated to the peers.

For example, the 192.168.0.0/24 prefix is announced to the peer with a
label value of 222.

> router bgp 65500
> [..]
>  neighbor 192.0.2.2 remote-as 65501
>  address-family ipv4-vpn
>   neighbor 192.0.2.2 activate
>  exit-address-family
> exit
> router bgp 65500 vrf vrf2
>  address-family ipv4 unicast
>   network 192.168.0.0/24
>   label vpn export 222
>   rd vpn export 444:444
>   rt vpn both 53:100
>   export vpn
>   import vpn
>  exit-address-family

Changing the label with "label vpn export" does not update the label
value to the peer unless the BGP sessions is re-established.

No labels are stored are stored struct bgp_adj_out so that it is
impossible to compare the current value with the previous value
in adj-RIB-out.

Reference the bgp_labels pointer in struct bgp_adj_out and compare the
values when updating adj-RIB-out.

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>
Signed-off-by: Louis Scalbert <louis.scalbert@6wind.com>

bgpd/bgp_advertise.h

@@ -75,6 +75,9 @@ struct bgp_adj_out {
 	/* Advertised attribute.  */
 	struct attr *attr;
 
+	/* VPN label information */
+	struct bgp_labels *labels;
+
 	/* Advertisement information.  */
 	struct bgp_advertise *adv;
 };

bgpd/bgp_updgrp_adv.c

@@ -78,6 +78,8 @@ static inline struct bgp_adj_out *adj_lookup(struct bgp_dest *dest,
 
 static void adj_free(struct bgp_adj_out *adj)
 {
+	bgp_labels_unintern(&adj->labels);
+
 	TAILQ_REMOVE(&(adj->subgroup->adjq), adj, subgrp_adj_train);
 	SUBGRP_DECR_STAT(adj->subgroup, adj_count);
 
@@ -572,7 +574,9 @@ bool bgp_adj_out_set_subgroup(struct bgp_dest *dest,
 		attr_hash = attrhash_key_make(attr);
 
 	if (!CHECK_FLAG(subgrp->sflags, SUBGRP_STATUS_FORCE_UPDATES) &&
-	    attr_hash && adj->attr_hash == attr_hash) {
+	    attr_hash && adj->attr_hash == attr_hash &&
+	    bgp_labels_cmp(path->extra ? path->extra->labels : NULL,
+			   adj->labels)) {
 		if (BGP_DEBUG(update, UPDATE_OUT)) {
 			char attr_str[BUFSIZ] = {0};
 
@@ -614,6 +618,10 @@ bool bgp_adj_out_set_subgroup(struct bgp_dest *dest,
 	adv->baa = bgp_advertise_attr_intern(subgrp->hash, attr);
 	adv->adj = adj;
 	adj->attr_hash = attr_hash;
+	if (path->extra)
+		adj->labels = bgp_labels_intern(path->extra->labels);
+	else
+		adj->labels = NULL;
 
 	/* Add new advertisement to advertisement attribute list. */
 	bgp_advertise_add(adv->baa, adv);