ArduCopter: ensure hover Z-bias message prints when EKF preloads correction

Since the EKF now loads hover Z-bias from INS params at init, the
correction is already set when vehicle code tries to apply it. Use a
one-shot flag to ensure the informational GCS message is still printed
for non-zero corrections, regardless of whether the EKF already has
the value.

Author: andyp1per

ArduCopter/Attitude.cpp

@@ -168,6 +168,8 @@ void Copter::init_hover_bias_correction(void)
 // called from one_hz_loop while disarmed until values match
 void Copter::set_hover_z_bias_correction(void)
 {
+    static bool message_sent;
+
     if ((g2.accel_zbias_learn & ACC_ZBIAS_LEARN_USE) == 0) {
         return;
     }
@@ -176,16 +178,17 @@ void Copter::set_hover_z_bias_correction(void)
         const float saved_bias = _hover_bias_learning[imu];
         const float current_correction = ahrs.get_hover_z_bias_correction(imu);
 
-        // Skip if already set correctly or nothing to set
-        if (is_equal(saved_bias, current_correction)) {
-            continue;
+        // Set the correction if not already matching
+        if (!is_equal(saved_bias, current_correction)) {
+            ahrs.set_hover_z_bias_correction(imu, saved_bias);
         }
 
-        // Try to set the correction
-        if (ahrs.set_hover_z_bias_correction(imu, saved_bias)) {
+        // Report non-zero corrections once (EKF may have loaded from params)
+        if (!message_sent && !is_zero(saved_bias)) {
             GCS_SEND_TEXT(MAV_SEVERITY_INFO, "Hover Z-bias IMU%u: %.3f m/s^2", imu, saved_bias);
         }
     }
+    message_sent = true;
 }
 
 // update_hover_bias_learning - learns Z-axis accelerometer bias during hover

ArduCopter/Parameters.cpp

@@ -1129,7 +1129,7 @@ const AP_Param::GroupInfo ParametersG2::var_info2[] = {
     // @Description: Bitmask controlling accelerometer Z-axis bias learning during hover to compensate for vibration rectification. Only active when using EKF3 (AHRS_EKF_TYPE=3). Bit 0: Learn bias during hover and save to EEPROM on disarm. Bit 1: Use saved bias values (apply correction to EKF). Bit 2: Disable EKF bias learning while disarmed (don't use zero velocity assumption on ground).
     // @Bitmask: 0:Learn and Save,1:Use Saved Values,2:Disable Ground Learning
     // @User: Advanced
-    AP_GROUPINFO("ACC_ZBIAS_LEARN", 17, ParametersG2, accel_zbias_learn, 3),
+    AP_GROUPINFO("ACC_ZBIAS_LEARN", 17, ParametersG2, accel_zbias_learn, 0),
 
     // @Param: TKOFF_GNDEFF_TMO
     // @DisplayName: Ground Effect Timeout