fixup! X on msgpack support

This is a fix of 1cf2712f:
'AppendString' is the equivalent to NEO/py 'NEO' encoding, not
'AppendBytes'.

go/neo/neonet/newlink.go

@@ -216,7 +216,7 @@ func _handshakeServer(ctx context.Context, conn net.Conn, version uint32) (enc p
 // handshake hello:
 //
 // - 00 00 00 <ver>	for 'N' encoding, and
-// - 92 c4 03 NEO ...	for 'M' encoding (= msgpack of (b"NEO", <ver>))
+// - 92 a3 NEO ...	for 'M' encoding (= msgpack of (b"NEO", <ver>))
 //
 // the first byte is different from TLS handshake (0x16).
 
@@ -234,9 +234,9 @@ func txHello(errctx string, conn net.Conn, version uint32, enc proto.Encoding) (
 		b[3] = uint8(version)
 
 	case 'M':
-		// (b"NEO", <V>) encoded as msgpack (= 92 c4 03 NEO int(<V>))
+		// (b"NEO", <V>) encoded as msgpack (= 92 a3 NEO int(<V>))
 		b = msgp.AppendArrayHeader(b, 2)       // 92
-		b = msgp.AppendBytes(b, []byte("NEO")) // c4 03 NEO
+		b = msgp.AppendString(b, "NEO")        // a3 NEO
 		b = msgp.AppendUint32(b, version)      // u?intX version
 
 	default: