device: set the reason for when deactivating for another activation

It's always user requested -- auto activation never happens on already active
devices. nm_device_release_one_slave() rightly asserts teardown with
(un)configuration does not happen for no reason at all.

https://bugzilla.gnome.org/show_bug.cgi?id=744812
(cherry picked from commit 600489003f)

src/devices/nm-device.c

@@ -5790,7 +5790,7 @@ nm_device_queue_activation (NMDevice *self, NMActRequest *req)
 		_LOGI (LOGD_DEVICE, "disconnecting for new activation request.");
 		nm_device_state_changed (self,
 		                         NM_DEVICE_STATE_DEACTIVATING,
-		                         NM_DEVICE_STATE_REASON_NONE);
+		                         NM_DEVICE_STATE_REASON_USER_REQUESTED);
 	}
 }