AP_NavEKF: added a getter function for active source set

libraries/AP_NavEKF/AP_NavEKF_Source.cpp

@@ -524,6 +524,12 @@ bool AP_NavEKF_Source::wheel_encoder_enabled(void) const
     return false;
 }
 
+// returns active source set
+uint8_t AP_NavEKF_Source::get_active_source_set() const
+{
+    return active_source_set;
+}
+
 // return true if GPS yaw is enabled on any source
 bool AP_NavEKF_Source::gps_yaw_enabled(void) const
 {

libraries/AP_NavEKF/AP_NavEKF_Source.h

@@ -103,6 +103,9 @@ public:
     // return true if wheel encoder is enabled on any source
     bool wheel_encoder_enabled(void) const;
 
+    // returns active source set 
+    uint8_t get_active_source_set() const;
+
     static const struct AP_Param::GroupInfo var_info[];
 
 private: