Linux: enabled commander module

The commander module now compiles for Linux.

state_machine_helper_linux.cpp iterates over the virtual devices vs
all devices under /dev as per NuttX when disabling publishing.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/drivers/device/vdev_posix.cpp

@@ -274,5 +274,10 @@ void px4_show_devices()
 	VDev::showDevices();
 }
 
+const char * px4_get_device_names(unsigned int *handle)
+{
+	return VDev::devList(handle);
+}
+
 }