Don't report that we saw an aircraft if it was probably just single-m…

…essage noise:

Only add to the "seen" set on DF11/17/18 messages (other types
have no CRC check).

Require two messages before reporting an aircraft.

This reinstates filtering that was done at the Python level before
the filter API was added.

mlat/client/coordinator.py

@@ -162,7 +162,7 @@ def update_aircraft(self, now):
         self.last_aircraft_update = now
 
     def send_aircraft_report(self):
-        all_aircraft = {x.icao for x in self.aircraft.values()}
+        all_aircraft = {x.icao for x in self.aircraft.values() if x.messages > 1}
         seen_ac = all_aircraft.difference(self.reported)
         lost_ac = self.reported.difference(all_aircraft)
 
@@ -195,6 +195,9 @@ def periodic_stats(self, now):
         adsb_req = adsb_total = modes_req = modes_total = 0
         now = monotonic_time()
         for ac in self.aircraft.values():
+            if ac.messages < 2:
+                continue
+
             if now - ac.last_position_time < self.position_expiry_age:
                 adsb_total += 1
                 if ac.requested:

modes_reader.c

@@ -1261,9 +1261,14 @@ static int filter_message(modesreader *self, PyObject *o)
     }
 
     if (self->seen != NULL && self->seen != Py_None) {
-        /* note that we saw this aircraft, even if the message is filtered */
-        if (PySet_Add(self->seen, message->address) < 0) {
-            return -1;
+        if (message->df == 11 || message->df == 17 || message->df == 18) {
+            /* note that we saw this aircraft, even if the message is filtered.
+             * only do this for CRC-checked messages as we get a lot of noise
+             * otherwise.
+             */
+            if (PySet_Add(self->seen, message->address) < 0) {
+                return -1;
+            }
         }
     }