uavcan escs: Modified esc_status reporting to have _rotor_count published.

Signed-off-by: Claudio Micheli <claudio@auterion.com>

src/lib/mixer/mixer.h

@@ -254,6 +254,8 @@ public:
 	 */
 	virtual void set_airmode(Airmode airmode) {};
 
+	virtual unsigned get_multirotor_count()  {return 0;}
+
 protected:
 	/** client-supplied callback used when fetching control values */
 	ControlCallback			_control_cb;
@@ -450,6 +452,8 @@ public:
 
 	void 	set_airmode(Airmode airmode) override;
 
+	unsigned get_multirotor_count() override;
+
 private:
 	Mixer				*_first;	/**< linked list of mixers */
 
@@ -715,6 +719,8 @@ public:
 
 	void 			set_airmode(Airmode airmode) override;
 
+	unsigned get_multirotor_count() override {return _rotor_count;}
+
 	union saturation_status {
 		struct {
 			uint16_t valid		: 1; // 0 - true when the saturation status is used

src/lib/mixer/mixer_group.cpp

@@ -198,6 +198,25 @@ MixerGroup::set_airmode(Airmode airmode)
 	}
 }
 
+unsigned
+MixerGroup::get_multirotor_count()
+{
+	Mixer	*mixer = _first;
+	unsigned rotor_count = 0;
+
+	while (mixer != nullptr) {
+
+		rotor_count = mixer->get_multirotor_count();
+
+		if (rotor_count > 0) {
+			break;
+
+		} else { mixer = mixer -> _next;}
+	}
+
+	return rotor_count;
+}
+
 uint16_t
 MixerGroup::get_saturation_status()
 {