udevadm: improve debug logging when triggering/watching events

Let's make debugging udev triggering a bit easier, by generating debug
log messages whenever we trigger a device, and also when we see the
event in pid1.

src/core/device.c

@@ -1142,6 +1142,8 @@ static int device_dispatch_io(sd_device_monitor *monitor, sd_device *dev, void *
                 return 0;
         }
 
+        log_device_debug(dev, "Got '%s' action on syspath '%s'.", device_action_to_string(action), sysfs);
+
         if (action == SD_DEVICE_MOVE)
                 device_remove_old_on_move(m, dev);
 

src/udev/udevadm-trigger.c

@@ -112,7 +112,8 @@ static int exec_list(
                         if (ret == 0 && !ignore)
                                 ret = r;
                         continue;
-                }
+                } else
+                        log_device_debug(d, "Triggered device with action '%s'.", action_str);
 
                 if (uuid_supported < 0)
                         uuid_supported = true;