[swss]: Update SwSS submodule (#829)

Shuotian Cheng · lguohan · commit 1857df2b086b · 2017-07-22T00:24:33.000-07:00
diff --git a/src/sonic-swss b/src/sonic-swss
@@ -1 +1 @@
-Subproject commit e521a358cea12966854a565ed8d1e4c4dc0c7605
+Subproject commit 4f606f575da80216eee7509e1e274d0d9be40595
