core: handle device removal when properties are unreadable

By the time we get the udev device removal notification we may not
be able to read properties, since the device has already been
removed from sysfs.  That means we can't get the ifindex, so we need
to fall back to the interface name.  But we always want to prefer
the ifindex since that will never change as long as the device is
connected, unlike the interface name.

src/nm-manager.c

@@ -2426,6 +2426,14 @@ udev_device_removed_cb (NMUdevManager *manager,
 
 	ifindex = g_udev_device_get_property_as_int (udev_device, "IFINDEX");
 	device = find_device_by_ifindex (self, ifindex);
+	if (!device) {
+		/* On removal we won't always be able to read properties anymore, as
+		 * they may have already been removed from sysfs.  Instead, we just
+		 * have to fall back to the device's interface name.
+		 */
+		device = find_device_by_iface (self, g_udev_device_get_name (udev_device));
+	}
+
 	if (device)
 		priv->devices = remove_one_device (self, priv->devices, device, FALSE);
 }