bgpd: Fix regression in args consolidation, total should be inited from args

* bgp_attr.c: (bgp_attr_unknown) total should be initialised from the args.
diff --git a/bgpd/bgp_attr.c b/bgpd/bgp_attr.c
index 0d82aba..81802ce 100644
--- a/bgpd/bgp_attr.c
+++ b/bgpd/bgp_attr.c
@@ -1646,7 +1646,7 @@
 static bgp_attr_parse_ret_t
 bgp_attr_unknown (struct bgp_attr_parser_args *args)
 {
-  bgp_size_t total;
+  bgp_size_t total = args->total;
   struct transit *transit;
   struct attr_extra *attre;
   struct peer *const peer = args->peer;