SITL: only report ground contact at most once per second

libraries/SITL/SIM_Aircraft.cpp

@@ -359,8 +359,9 @@ void Aircraft::update_dynamics(const Vector3f &rot_accel)
 
     // constrain height to the ground
     if (on_ground(position)) {
-        if (!on_ground(old_position)) {
+        if (!on_ground(old_position) && AP_HAL::millis() - last_ground_contact_ms > 1000) {
             printf("Hit ground at %f m/s\n", velocity_ef.z);
+            last_ground_contact_ms = AP_HAL::millis();
         }
         position.z = -(ground_level + frame_height - home.alt*0.01f);
     }

libraries/SITL/SIM_Aircraft.h

@@ -159,6 +159,7 @@ protected:
 private:
     uint64_t last_time_us = 0;
     uint32_t frame_counter = 0;
+    uint32_t last_ground_contact_ms;
     const uint32_t min_sleep_time;
 };