AntennaTracker: ignore MSG_AOA_SSA

AntennaTracker/GCS_Mavlink.cpp

@@ -271,6 +271,7 @@ bool GCS_MAVLINK_Tracker::try_send_message(enum ap_message id)
     case MSG_RPM:
     case MSG_MISSION_ITEM_REACHED:
     case MSG_POSITION_TARGET_GLOBAL_INT:
+    case MSG_AOA_SSA:
         break; // just here to prevent a warning
     }
     return true;