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.cpp

@@ -467,5 +467,13 @@ void VDev::showDevices()
 	}
 }
 
+const char *VDev::devList(unsigned int *next)
+{
+	for (;*next<PX4_MAX_DEV; (*next)++)
+		if (devmap[*next])
+			return devmap[(*next)++]->name;
+	return NULL;
+}
+
 } // namespace device