omit length bytes from flag data

protocol/esta/acn/pdu.cpp

@@ -155,7 +155,7 @@ size_t Pdu::streamSize() const
 void Pdu::iStream(Stream stream)
 {
   // get the flags
-  flags_._raw = stream->peek();
+  flags_._raw = stream->peek() & 0xf0;      // high 4 bits are flags
 
   // get the length
   size_t length;