Tracker: make set_home bool, do not save bad homes

AntennaTracker/AntennaTracker.cpp

@@ -111,7 +111,9 @@ void Tracker::one_second_loop()
         // set home to current location
         Location temp_loc;
         if (ahrs.get_location(temp_loc)) {
-            set_home(temp_loc);
+            if (!set_home(temp_loc)){
+                // fail silently
+            }
         }
     }
 

AntennaTracker/GCS_Mavlink.cpp

@@ -470,7 +470,10 @@ void GCS_MAVLINK_Tracker::handleMessage(mavlink_message_t* msg)
 
         // check if this is the HOME wp
         if (packet.seq == 0) {
-            tracker.set_home(tell_command); // New home in EEPROM
+            if (!tracker.set_home(tell_command)) {
+                result = MAV_MISSION_ERROR;
+                goto mission_failed;
+            }
             send_text(MAV_SEVERITY_INFO,"New HOME received");
             waypoint_receiving = false;
         }

AntennaTracker/Tracker.h

@@ -251,8 +251,8 @@ private:
     // system.cpp
     void init_tracker();
     bool get_home_eeprom(struct Location &loc);
-    void set_home_eeprom(struct Location temp);
-    void set_home(struct Location temp);
+    bool set_home_eeprom(const Location &temp) WARN_IF_UNUSED;
+    bool set_home(const Location &temp) WARN_IF_UNUSED;
     void arm_servos();
     void disarm_servos();
     void prepare_servos();

AntennaTracker/sensors.cpp

@@ -71,7 +71,9 @@ void Tracker::update_GPS(void)
                 // Now have an initial GPS position
                 // use it as the HOME position in future startups
                 current_loc = gps.location();
-                set_home(current_loc);
+                if (!set_home(current_loc)) {
+                    // silently ignored
+                }
 
                 if (g.compass_enabled) {
                     // Set compass declination automatically

AntennaTracker/system.cpp

@@ -135,7 +135,7 @@ bool Tracker::get_home_eeprom(struct Location &loc)
     return true;
 }
 
-void Tracker::set_home_eeprom(struct Location temp)
+bool Tracker::set_home_eeprom(const Location &temp)
 {
     wp_storage.write_byte(0, 0);
     wp_storage.write_uint32(1, temp.alt);
@@ -144,20 +144,26 @@ void Tracker::set_home_eeprom(struct Location temp)
 
     // Now have a home location in EEPROM
     g.command_total.set_and_save(1); // At most 1 entry for HOME
+    return true;
 }
 
-void Tracker::set_home(struct Location temp)
+bool Tracker::set_home(const Location &temp)
 {
-    set_home_eeprom(temp);
-    current_loc = temp;
-
     // check EKF origin has been set
     Location ekf_origin;
     if (ahrs.get_origin(ekf_origin)) {
         if (!ahrs.set_home(temp)) {
-            // ignore error silently
+            return false;
         }
     }
+
+    if (!set_home_eeprom(temp)) {
+        return false;
+    }
+
+    current_loc = temp;
+
+    return true;
 }
 
 void Tracker::arm_servos()