core: slim down `common.hpp`

Change-Id: I875c35147edd2261fbaa24e809c170d5cd9b94d3
diff --git a/daemon/face/ethernet-channel.cpp b/daemon/face/ethernet-channel.cpp
index dfd5bf3..1ac0625 100644
--- a/daemon/face/ethernet-channel.cpp
+++ b/daemon/face/ethernet-channel.cpp
@@ -217,7 +217,7 @@
   if (!isListening())
     return;
 
-  std::string filter = "(ether proto " + to_string(ethernet::ETHERTYPE_NDN) +
+  std::string filter = "(ether proto " + std::to_string(ethernet::ETHERTYPE_NDN) +
                        ") && (ether dst " + m_localEndpoint->getEthernetAddress().toString() + ")";
   for (const auto& addr : m_channelFaces | boost::adaptors::map_keys) {
     filter += " && (not ether src " + addr.toString() + ")";