bgpd: don't use BGP_ATTR_VNC(255) unless ENABLE_BGP_VNC_ATTR is defined

Signed-off-by: Lou Berger <lberger@labn.net>
static void cluster_init(void)
{
	cluster_hash = hash_create(cluster_hash_key_make, cluster_hash_cmp,
				   "BGP Cluster");
}

static void cluster_init(void)
{
	cluster_hash = hash_create(cluster_hash_key_make, cluster_hash_cmp,
				   "BGP Cluster");
}
