bgpd: bestpath failure when you have a singlepath not in holddown

When you have multiple paths to a particular route and a single
path changes.  In addition of the other paths are either in
hold down or not established or really just not selected you
could end up with a situation where the bestpath choosen
was a path that was in hold down.

Modify the code such that when there is nothing worse
in bestpath selection for the choosen path, but were
unable to do any sorting, just put the path on the top
of the list and declare it the winner.  Else just
do the original and put it at the end.

Signed-off-by: Chirag Shah <[email protected]>
Signed-off-by: Donald Sharp <[email protected]>

bgpd/bgp_route.c

@@ -3198,15 +3198,23 @@ void bgp_best_selection(struct bgp *bgp, struct bgp_dest *dest,
 			struct bgp_path_info *end =
 				bgp_dest_get_bgp_path_info(dest);
 
-			for (; end && end->next != NULL; end = end->next)
-				;
+			if (end && any_comparisons) {
+				for (; end && end->next != NULL; end = end->next)
+					;
 
-			if (end)
-				end->next = first;
-			else
+				if (end)
+					end->next = first;
+				else
+					bgp_dest_set_bgp_path_info(dest, first);
+				first->prev = end;
+				first->next = NULL;
+			} else {
 				bgp_dest_set_bgp_path_info(dest, first);
-			first->prev = end;
-			first->next = NULL;
+				if (end)
+					end->prev = first;
+				first->next = end;
+				first->prev = NULL;
+			}
 
 			dest->reason = first->reason;
 		} else {