proto: Dump protocol version to post-msgpack version

NOTE: We may need to differentiate between the last N version (6) and
the msgpack version (currently 0) in order to make auto-detection of
encoding still workable (e.g. to still provide backwards-compatibility
- to connect with an older NEO cluster).

go/neo/proto/proto.go

@@ -77,7 +77,7 @@ import (
 const (
 	// The protocol version must be increased whenever upgrading a node may require
 	// to upgrade other nodes.
-	Version = 6
+	Version = 0
 
 	// length of packet header in 'N'-encoding
 	PktHeaderLenN = 10 // = unsafe.Sizeof(PktHeaderN{}), but latter gives typed constant (uintptr)