AP_NavEKF: Link process noise to arm status, not pos hold mode

libraries/AP_NavEKF/AP_NavEKF.cpp

@@ -1213,10 +1213,10 @@ void NavEKF::CovariancePrediction()
     }
     for (uint8_t i= 0; i<=9;  i++) processNoise[i] = 1.0e-9f;
     for (uint8_t i=10; i<=12; i++) processNoise[i] = dAngBiasSigma;
-    // scale gyro bias noise when in position hold mode to allow for faster bias estimation
+    // scale gyro bias noise when disarmed to allow for faster bias estimation
     for (uint8_t i=10; i<=12; i++) {
         processNoise[i] = dAngBiasSigma;
-        if (posHoldMode) {
+        if (!vehicleArmed) {
             processNoise[i] *= _gyroBiasNoiseScaler;
         }
     }