px4_work_queue: command line status output and shutdown empty queues

* adds a work_queue systemcmd that will bring a tree view of all active work queues and work items
 * WorkQueues now track attached WorkItems and will shutdown when the last WorkItem is detached

src/lib/mixer_module/CMakeLists.txt

@@ -32,4 +32,3 @@
 ############################################################################
 
 px4_add_library(mixer_module mixer_module.cpp)
-

src/lib/mixer_module/mixer_module.cpp

@@ -524,4 +524,3 @@ int MixingOutput::loadMixerThreadSafe(const char *buf, unsigned len)
 
 	return _command.result;
 }
-

src/lib/mixer_module/mixer_module.hpp

@@ -61,8 +61,8 @@ class OutputModuleInterface : public px4::ScheduledWorkItem, public ModuleParams
 public:
 	static constexpr int MAX_ACTUATORS = DIRECT_PWM_OUTPUT_CHANNELS;
 
-	OutputModuleInterface(const px4::wq_config_t &config)
-		: px4::ScheduledWorkItem(config), ModuleParams(nullptr) {}
+	OutputModuleInterface(const char *name, const px4::wq_config_t &config)
+		: px4::ScheduledWorkItem(name, config), ModuleParams(nullptr) {}
 
 	virtual void updateOutputs(bool stop_motors, uint16_t outputs[MAX_ACTUATORS],
 				   unsigned num_outputs, unsigned num_control_groups_updated) = 0;
@@ -239,4 +239,3 @@ private:
 
 	)
 };
-