Replace virtual methods with static attributes, chainparams.h depends on

protocol.h instead of the other way around

src/protocol.h

@@ -10,7 +10,6 @@
 #ifndef __INCLUDED_PROTOCOL_H__
 #define __INCLUDED_PROTOCOL_H__
 
-#include "chainparams.h"
 #include "netbase.h"
 #include "serialize.h"
 #include "uint256.h"
@@ -19,6 +18,8 @@
 #include <stdint.h>
 #include <string>
 
+#define MESSAGE_START_SIZE 4
+
 /** Message header.
  * (4) message start.
  * (12) command.