HNSW search use efSearch from params if provided (#3233)

Summary:
I found that HNSW search method uses its own efSearch to create candidates, which should be got from params if provided I think?

Pull Request resolved: #3233

Reviewed By: algoriddle

Differential Revision: D53342879

Pulled By: mdouze

fbshipit-source-id: 4f47f19d3673d1bb8d7e8e82745f9e5c1b9afb42

faiss/impl/HNSW.cpp

@@ -829,7 +829,7 @@ HNSWStats HNSW::search(
             greedy_update_nearest(*this, qdis, level, nearest, d_nearest);
         }
 
-        int ef = std::max(efSearch, k);
+        int ef = std::max(params ? params->efSearch : efSearch, k);
         if (search_bounded_queue) { // this is the most common branch
             MinimaxHeap candidates(ef);