Connection::Receive(): receive Network Packet instead of SharedBuffer<u8>.

Because we get a Buffer<u8> from ConnectionEvent, don't convert it to SharedBuffer<u8> and return it to Server/Client::Receive which will convert it to NetworkPacket
Instead, put the Buffer<u8> directly to NetworkPacket and return it to packet processing
This remove a long existing memory copy
Also check the packet size directly into Connection::Receive instead of packet processing

src/server.h

@@ -219,7 +219,7 @@ public:
 	void handleCommand_NodeMetaFields(NetworkPacket* pkt);
 	void handleCommand_InventoryFields(NetworkPacket* pkt);
 
-	void ProcessData(u8 *data, u32 datasize, u16 peer_id);
+	void ProcessData(NetworkPacket *pkt);
 
 	void Send(NetworkPacket* pkt);