MINOR: server: Handle weight increase in consistent hash.

When the server weight is rised using the CLI, extra nodes have to be
allocated, or the weight will be effectively the same as the original one.

[wt: given that the doc made no explicit mention about this limitation,
this patch could even be backported as it fixes an unexpected behaviour]

src/lb_chash.c

@@ -78,6 +78,25 @@ static inline void chash_queue_dequeue_srv(struct server *s)
 		eb32_delete(&s->lb_nodes[s->lb_nodes_now].node);
 	}
 
+	/* Attempt to increase the total number of nodes, if the user
+	 * increased the weight beyond the original weight
+	 */
+	if (s->lb_nodes_tot < s->next_eweight) {
+		struct tree_occ *new_nodes = realloc(s->lb_nodes, s->next_eweight);
+
+		if (new_nodes) {
+			unsigned int j;
+
+			s->lb_nodes = new_nodes;
+			memset(&s->lb_nodes[s->lb_nodes_tot], 0,
+			    (s->next_eweight - s->lb_nodes_tot) * sizeof(*s->lb_nodes));
+			for (j = s->lb_nodes_tot; j < s->next_eweight; j++) {
+				s->lb_nodes[j].server = s;
+				s->lb_nodes[j].node.key = full_hash(s->puid * SRV_EWGHT_RANGE + j);
+			}
+			s->lb_nodes_tot = s->next_eweight;
+		}
+	}
 	while (s->lb_nodes_now < s->next_eweight) {
 		if (s->lb_nodes_now >= s->lb_nodes_tot) // should always be false anyway
 			break;