AP_NavEKF3: added a getter function to infer the source index used by ekf3

libraries/AP_NavEKF3/AP_NavEKF3.cpp

@@ -1239,6 +1239,12 @@ void NavEKF3::getAccelBias(int8_t instance, Vector3f &accelBias) const
     }
 }
 
+// returns active source set used by EKF3
+uint8_t NavEKF3::get_active_source_set() const
+{
+    return sources.get_active_source_set();
+}
+
 // reset body axis gyro bias estimates
 void NavEKF3::resetGyroBias(void)
 {

libraries/AP_NavEKF3/AP_NavEKF3.h

@@ -97,6 +97,9 @@ public:
     // An out of range instance (eg -1) returns data for the primary instance
     void getAccelBias(int8_t instance, Vector3f &accelBias) const;
 
+    //returns index of the active source set used
+    uint8_t get_active_source_set() const;
+
     // reset body axis gyro bias estimates
     void resetGyroBias(void);