build: make precompiled headers more useful

This can reduce the compilation time of a release
build (without tests) by more than 40%

Refs: #5212
Change-Id: I977aff0c0c7becbfee8a8b55605b81d0c014829b
diff --git a/core/network.cpp b/core/network.cpp
index bfecec5..5e75b7f 100644
--- a/core/network.cpp
+++ b/core/network.cpp
@@ -25,9 +25,13 @@
 
 #include "network.hpp"
 
+#include <boost/lexical_cast.hpp>
 #include <boost/utility/value_init.hpp>
+
 #include <algorithm>
 #include <cctype>
+#include <istream>
+#include <ostream>
 
 namespace nfd {