Make protocol message counters more granular:

A running instance of the server tracks the number of protocol messages
and the number of bytes it sends and receives.

This commit makes the counters more granular, allowing server operators
to better track and understand bandwidth usage.

src/ripple/overlay/impl/Message.cpp

@@ -39,8 +39,7 @@ Message::Message (::google::protobuf::Message const& message, int type)
         message.SerializeToArray (&mBuffer [Message::kHeaderBytes], messageBytes);
     }
 
-    mCategory = safe_cast<int>(TrafficCount::categorize
-        (message, type, false));
+    mCategory = TrafficCount::categorize(message, type, false);
 }
 
 bool Message::operator== (Message const& other) const