Add isLanding function

Checking for landing is used for a security purpose. If landing procedure is
triggered but not by the swarm management script, it means it has been triggered
externally most probably for emergency reason.

mavsdk_wrapper.cpp

@@ -56,8 +56,9 @@ static const float DEFAULT_SPEED = 17;
 static float last_override_altitude;
 static float last_override_speed;
 
-static bool first_coordinate_entered = false;
 static bool do_projection = false;
+static bool first_coordinate_entered = false;
+static bool is_in_air = false;
 
 // Logs functions
 
@@ -300,6 +301,12 @@ int start(const char * ip, int port, const char * log_file, int timeout) {
         current_position[4] = position.time_boot_ms + timestamp_difference;
     });
 
+    telemetry->subscribe_landed_state([](const Telemetry::LandedState landed_state) {
+        if (landed_state == Telemetry::LandedState::InAir) {
+            is_in_air = true;
+        }
+    });
+
     do {
         log("Waiting for first telemetry");
         sleep_for(seconds(1));
@@ -479,11 +486,17 @@ float getClimbRate(void) {
     return telemetry->fixedwing_metrics().climb_rate_m_s;
 }
 
+int gpsIsOk(void) {
+    Telemetry::FixType fixType = telemetry->gps_info().fix_type;
+    return (fixType != Telemetry::FixType::NoGps) && (fixType != Telemetry::FixType::NoFix);
+}
+
 int healthAllOk(void) {
     return telemetry->health_all_ok();
 }
 
-int gpsIsOk(void) {
-    Telemetry::FixType fixType = telemetry->gps_info().fix_type;
-    return (fixType != Telemetry::FixType::NoGps) && (fixType != Telemetry::FixType::NoFix);
+int isLanding(void) {
+    if (is_in_air && telemetry->landed_state() != Telemetry::LandedState::InAir)
+        return 1;
+    return 0;
 }