bgpd: fix bgp label evpn CID 1636504

bgpd: fix bgp label evpn CID 1636504

The following static analysis can be seen :

> *** CID 1636504:    (ARRAY_VS_SINGLETON)
> /bgpd/bgp_evpn_mh.c: 1241 in bgp_evpn_type1_route_process()
> 1235            build_evpn_type1_prefix(&p, eth_tag, &esi, vtep_ip);
> 1236            /* Process the route. */
> 1237            if (attr) {
> 1238                    bgp_update(peer, (struct prefix *)&p, addpath_id, attr, afi, safi, ZEBRA_ROUTE_BGP,
> 1239                               BGP_ROUTE_NORMAL, &prd, &label, num_labels, 0, NULL);
> 1240            } else {
> >>>     CID 1636504:    (ARRAY_VS_SINGLETON)
> >>>     Passing "&label" to function "bgp_withdraw" which uses it as an array. This might corrupt or misinterpret adjacent memory locations.
> 1241                    bgp_withdraw(peer, (struct prefix *)&p, addpath_id, afi, safi, ZEBRA_ROUTE_BGP,
> 1242                                 BGP_ROUTE_NORMAL, &prd, &label, num_labels);
> 1243            }
> 1244            return 0;
> 1245     }
> 1246
> /bgpd/bgp_evpn_mh.c: 1238 in bgp_evpn_type1_route_process()
> 1232             * table
> 1233             */
> 1234            vtep_ip.s_addr = INADDR_ANY;
> 1235            build_evpn_type1_prefix(&p, eth_tag, &esi, vtep_ip);
> 1236            /* Process the route. */
> 1237            if (attr) {
> >>>     CID 1636504:    (ARRAY_VS_SINGLETON)
> >>>     Passing "&label" to function "bgp_update" which uses it as an array. This might corrupt or misinterpret adjacent memory locations.
> 1238                    bgp_update(peer, (struct prefix *)&p, addpath_id, attr, afi, safi, ZEBRA_ROUTE_BGP,
> 1239                               BGP_ROUTE_NORMAL, &prd, &label, num_labels, 0, NULL);
> 1240            } else {
> 1241                    bgp_withdraw(peer, (struct prefix *)&p, addpath_id, afi, safi, ZEBRA_ROUTE_BGP,
> 1242                                 BGP_ROUTE_NORMAL, &prd, &label, num_labels);
> 1243            }

Fix this by declaring a label array instead of a single array.

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>
(cherry picked from commit ba462af2e3a4a242b2ffcde6074750f851632777)