Plane: Rearrange header to save flash

Saves 392 bytes of flash on CubeBlack builds without increasing RAM
consumption at all. This also translates to a speed up as some of these
are looked up every loop multiple times.

ArduPlane/Plane.h

@@ -356,13 +356,13 @@ private:
     struct {
         // Used to track if the value on channel 3 (throtttle) has fallen below the failsafe threshold
         // RC receiver should be set up to output a low throttle value when signal is lost
-        bool rc_failsafe:1;
+        bool rc_failsafe;
 
         // has the saved mode for failsafe been set?
-        bool saved_mode_set:1;
+        bool saved_mode_set;
 
         // true if an adsb related failsafe has occurred
-        bool adsb:1;
+        bool adsb;
 
         // saved flight mode
         enum Mode::Number saved_mode_number;
@@ -467,59 +467,26 @@ private:
         uint32_t accel_event_ms;
         uint32_t start_time_ms;
     } takeoff_state;
-    
+
     // ground steering controller state
     struct {
         // Direction held during phases of takeoff and landing centidegrees
         // A value of -1 indicates the course has not been set/is not in use
         // this is a 0..36000 value, or -1 for disabled
-        int32_t hold_course_cd;
+        int32_t hold_course_cd = -1;
 
         // locked_course and locked_course_cd are used in stabilize mode 
         // when ground steering is active, and for steering in auto-takeoff
         bool locked_course;
         float locked_course_err;
-    } steer_state { -1, false, 0 };
+    } steer_state;
 
     // flight mode specific
     struct {
-        // Flag for using gps ground course instead of INS yaw.  Set false when takeoff command in process.
-        bool takeoff_complete:1;
-
-        // are we headed to the land approach waypoint? Works for any nav type
-        bool wp_is_land_approach:1;
-
-        // should we fly inverted?
-        bool inverted_flight:1;
-
-        // should we enable cross-tracking for the next waypoint?
-        bool next_wp_crosstrack:1;
-
-        // should we use cross-tracking for this waypoint?
-        bool crosstrack:1;
-
-        // in FBWA taildragger takeoff mode
-        bool fbwa_tdrag_takeoff_mode:1;
-
-        // have we checked for an auto-land?
-        bool checked_for_autoland:1;
-
-        // Altitude threshold to complete a takeoff command in autonomous modes.  Centimeters
-        // are we in idle mode? used for balloon launch to stop servo
-        // movement until altitude is reached
-        bool idle_mode:1;
-
-        // used to 'wiggle' servos in idle mode to prevent them freezing
-        // at high altitudes
-        uint8_t idle_wiggle_stage;
-
         // Altitude threshold to complete a takeoff command in autonomous
         // modes.  Centimeters above home
         int32_t takeoff_altitude_rel_cm;
 
-        // Minimum pitch to hold during takeoff command execution.  Hundredths of a degree
-        int16_t takeoff_pitch_cd;
-
         // Begin leveling out the enforced takeoff pitch angle min at this height to reduce/eliminate overshoot
         int32_t height_below_takeoff_to_level_off_cm;
 
@@ -527,9 +494,6 @@ private:
         // to control ground takeoff
         float highest_airspeed;
         
-        // initial pitch. Used to detect if nose is rising in a tail dragger
-        int16_t initial_pitch_cd;
-        
         // turn angle for next leg of mission
         float next_turn_angle {90};
 
@@ -554,11 +518,47 @@ private:
         // barometric altitude at start of takeoff
         float baro_takeoff_alt;
 
+        // initial pitch. Used to detect if nose is rising in a tail dragger
+        int16_t initial_pitch_cd;
+
+        // Minimum pitch to hold during takeoff command execution.  Hundredths of a degree
+        int16_t takeoff_pitch_cd;
+
+        // used to 'wiggle' servos in idle mode to prevent them freezing
+        // at high altitudes
+        uint8_t idle_wiggle_stage;
+
+        // Flag for using gps ground course instead of INS yaw.  Set false when takeoff command in process.
+        bool takeoff_complete;
+
+        // are we headed to the land approach waypoint? Works for any nav type
+        bool wp_is_land_approach;
+
+        // should we fly inverted?
+        bool inverted_flight;
+
+        // should we enable cross-tracking for the next waypoint?
+        bool next_wp_crosstrack;
+
+        // should we use cross-tracking for this waypoint?
+        bool crosstrack;
+
+        // in FBWA taildragger takeoff mode
+        bool fbwa_tdrag_takeoff_mode;
+
+        // have we checked for an auto-land?
+        bool checked_for_autoland;
+
+        // Altitude threshold to complete a takeoff command in autonomous modes.  Centimeters
+        // are we in idle mode? used for balloon launch to stop servo
+        // movement until altitude is reached
+        bool idle_mode;
+
         // are we in VTOL mode in AUTO?
-        bool vtol_mode:1;
+        bool vtol_mode;
 
         // are we doing loiter mode as a VTOL?
-        bool vtol_loiter:1;
+        bool vtol_loiter;
     } auto_state;
 
     struct {
@@ -583,13 +583,13 @@ private:
     struct {
         // on hard landings, only check once after directly a landing so you
         // don't trigger a crash when picking up the aircraft
-        bool checkedHardLanding:1;
+        bool checkedHardLanding;
 
         // crash detection. True when we are crashed
-        bool is_crashed:1;
+        bool is_crashed;
 
         // impact detection flag. Expires after a few seconds via impact_timer_ms
-        bool impact_detected:1;
+        bool impact_detected;
 
         // debounce timer
         uint32_t debounce_timer_ms;
@@ -771,7 +771,7 @@ private:
         uint32_t last_elev_check_us;
     } target_altitude {};
 
-    float relative_altitude = 0.0f;
+    float relative_altitude;
 
     // INS variables
     // The main loop execution time.  Seconds