p2p: make this work with boost <= 1.65 (pffff)

src/p2p/net_node.inl

@@ -1497,7 +1497,11 @@ namespace nodetool
           if (actual_ip.is_v4_mapped())
           {
             boost::asio::ip::address_v4 v4ip = make_address_v4_from_v6(actual_ip);
+#if BOOST_VERSION >= 106600
             return epee::net_utils::ipv4_network_address(v4ip.to_uint(), 0).host_str();
+#else
+            return epee::net_utils::ipv4_network_address(v4ip.to_ulong(), 0).host_str();
+#endif
           }
         }
         return address.host_str();