types: Migrate to stdplus ip

Change-Id: I777aa701204b0c4dbe5f0088cc2e6a4deb4f5d15
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/system_queries.cpp b/src/system_queries.cpp
index e922504..f58493a 100644
--- a/src/system_queries.cpp
+++ b/src/system_queries.cpp
@@ -17,6 +17,7 @@
 #include <optional>
 #include <stdexcept>
 #include <string_view>
+#include <unordered_set>
 
 namespace phosphor::network::system
 {