AP_Landing: abstract out init_start_nav_cnd work to landing lib

This reverts commit 3e89580383 and fixes it

libraries/AP_Landing/AP_Landing.cpp

@@ -186,6 +186,19 @@ void AP_Landing::setup_landing_glide_slope(const Location &prev_WP_loc, const Lo
     }
 }
 
+/*
+ * initialize state for new nav command
+ */
+void AP_Landing::init_start_nav_cmd(void)
+{
+    switch (type) {
+    default:
+    case TYPE_STANDARD_GLIDE_SLOPE:
+        type_slope_init_start_nav_cmd();
+        break;
+    }
+}
+
 /*
      Restart a landing by first checking for a DO_LAND_START and
      jump there. Otherwise decrement waypoint so we would re-start

libraries/AP_Landing/AP_Landing.h

@@ -89,6 +89,7 @@ public:
     int8_t get_abort_throttle_enable(void) const { return abort_throttle_enable; }
     int8_t get_flap_percent(void) const { return flap_percent; }
     int8_t get_throttle_slewrate(void) const { return throttle_slewrate; }
+    void init_start_nav_cmd(void);
 
 
     // Flag to indicate if we have landed.
@@ -110,14 +111,14 @@ public:
     // landing altitude offset (meters)
     float alt_offset;
 
-    // once landed, post some landing statistics to the GCS
-    bool post_stats;
-
     // denotes if a go-around has been commanded for landing
     bool commanded_go_around;
 
 private:
 
+    // once landed, post some landing statistics to the GCS
+    bool post_stats;
+
     bool has_aborted_due_to_slope_recalc;
 
     AP_Mission &mission;
@@ -157,5 +158,6 @@ private:
 
     void type_slope_setup_landing_glide_slope(const Location &prev_WP_loc, const Location &next_WP_loc, const Location &current_loc, int32_t &target_altitude_offset_cm);
     void type_slope_check_if_need_to_abort(const AP_Vehicle::FixedWing::Rangefinder_State &rangefinder_state);
+    void type_slope_init_start_nav_cmd(void);
 
 };

libraries/AP_Landing/AP_Landing_Slope.cpp

@@ -292,3 +292,15 @@ void AP_Landing::type_slope_setup_landing_glide_slope(const Location &prev_WP_lo
     // stay within the range of the start and end locations in altitude
     constrain_target_altitude_location_fn(loc, prev_WP_loc);
 }
+
+void AP_Landing::type_slope_init_start_nav_cmd(void)
+{
+    complete = false;
+    pre_flare = false;
+
+    // if a go around had been commanded, clear it now.
+    commanded_go_around = false;
+
+    // once landed, post some landing statistics to the GCS
+    post_stats = false;
+}