dht: unify bootstrapSearch and refill method

Since bootstrapSearch was rewritten to use the node cache, it made it clear that
refill should be rewritten as such. However, then bootstrapSearch becomes
irrelevant.

An enhancement to refill is that it will let insertNode review its whole list
of nodes and then let it insert nodes up to SEARCH_NODES nodes. The previous
method would not garantee this behavior since, most of the times, it would pass
less than SEARCH_NODES nodes to insertNode.

src/node_cache.cpp

@@ -34,19 +34,19 @@ NodeCache::getNode(const InfoHash& id, const sockaddr* sa, socklen_t sa_len, tim
 }
 
 std::vector<std::shared_ptr<Node>>
-NodeCache::getCachedNodes(const InfoHash& id, sa_family_t sa_f, size_t total) {
+NodeCache::getCachedNodes(const InfoHash& id, sa_family_t sa_f, size_t count) {
     const auto& c = (sa_f == AF_INET ? cache_4 : cache_6);
     auto it_p = c.lower_bound(id),
          it_n = it_p;
 
     std::vector<std::shared_ptr<Node>> nodes;
-    nodes.reserve(std::min(c.size(), total));
+    nodes.reserve(std::min(c.size(), count));
     NodeMap::const_iterator it;
 
     if (it_p != c.begin()) /* Create 2 separate iterator if we could */
         --it_p;
 
-    while (nodes.size() < total and (it_n != c.end() or it_p != c.end())) {
+    while (nodes.size() < count and (it_n != c.end() or it_p != c.end())) {
         /* If one of the iterator is at the end, then take the other one
            If they are both in middle of somewhere comapre both and take
            the closest to the id. */