* fix: init rx_air_time to 0

src/Dispatcher.h

@@ -134,7 +134,9 @@ protected:
   Dispatcher(Radio& radio, MillisecondClock& ms, PacketManager& mgr)
     : _radio(&radio), _ms(&ms), _mgr(&mgr)
   {
-    outbound = NULL; total_air_time = 0; next_tx_time = 0;
+    outbound = NULL;
+    total_air_time = rx_air_time = 0;
+    next_tx_time = 0;
     cad_busy_start = 0;
     next_floor_calib_time = next_agc_reset_time = 0;
     _err_flags = 0;