* new PAYLOAD_TYPE_CONTROL (11)

* repeater: onControlDataRecv(), now responds to new CTL_TYPE_NODE_DISCOVER_REQ (zero hop only)
* node prefs: new discovery_mod_timestamp  (will be set to affect when node should respond to DISCOVERY_REQ's )

src/Packet.h

@@ -27,6 +27,7 @@ namespace mesh {
 #define PAYLOAD_TYPE_PATH        0x08    // returned path (prefixed with dest/src hashes, MAC) (enc data: path, extra)
 #define PAYLOAD_TYPE_TRACE       0x09    // trace a path, collecting SNI for each hop
 #define PAYLOAD_TYPE_MULTIPART   0x0A    // packet is one of a set of packets
+#define PAYLOAD_TYPE_CONTROL     0x0B    // a control/discovery packet
 //...
 #define PAYLOAD_TYPE_RAW_CUSTOM   0x0F    // custom packet as raw bytes, for applications with custom encryption, payloads, etc