ipv6: recreate ipv6 link-local addresses when increasing MTU over IPV6_MIN_MTU

This change makes it so that we reinitialize the interface if the MTU is
increased back above IPV6_MIN_MTU and the interface is up.

Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -3147,6 +3147,32 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 		}
 		break;
 
+	case NETDEV_CHANGEMTU:
+		/* if MTU under IPV6_MIN_MTU stop IPv6 on this interface. */
+		if (dev->mtu < IPV6_MIN_MTU) {
+			addrconf_ifdown(dev, 1);
+			break;
+		}
+
+		if (idev) {
+			rt6_mtu_change(dev, dev->mtu);
+			idev->cnf.mtu6 = dev->mtu;
+			break;
+		}
+
+		/* allocate new idev */
+		idev = ipv6_add_dev(dev);
+		if (IS_ERR(idev))
+			break;
+
+		/* device is still not ready */
+		if (!(idev->if_flags & IF_READY))
+			break;
+
+		run_pending = 1;
+
+		/* fall through */
+
 	case NETDEV_UP:
 	case NETDEV_CHANGE:
 		if (dev->flags & IFF_SLAVE)
@@ -3170,7 +3196,7 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 				idev->if_flags |= IF_READY;
 				run_pending = 1;
 			}
-		} else {
+		} else if (event == NETDEV_CHANGE) {
 			if (!addrconf_qdisc_ok(dev)) {
 				/* device is still not ready. */
 				break;
@@ -3235,24 +3261,6 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 		}
 		break;
 
-	case NETDEV_CHANGEMTU:
-		if (idev && dev->mtu >= IPV6_MIN_MTU) {
-			rt6_mtu_change(dev, dev->mtu);
-			idev->cnf.mtu6 = dev->mtu;
-			break;
-		}
-
-		if (!idev && dev->mtu >= IPV6_MIN_MTU) {
-			idev = ipv6_add_dev(dev);
-			if (!IS_ERR(idev))
-				break;
-		}
-
-		/*
-		 * if MTU under IPV6_MIN_MTU.
-		 * Stop IPv6 on this interface.
-		 */
-
 	case NETDEV_DOWN:
 	case NETDEV_UNREGISTER:
 		/*