IPV6: Restore IPv6 when MTU is big enough

[IPV6]: Restore IPv6 when MTU is big enough

[ Upstream commit: d31c7b8f ]

Avaid provided test application, so bug got fixed.

IPv6 addrconf removes ipv6 inner device from netdev each time cmu
changes and new value is less than IPV6_MIN_MTU (1280 bytes).
When mtu is changed and new value is greater than IPV6_MIN_MTU,
it does not add ipv6 addresses and inner device bac.

This patch fixes that.

Tested with Avaid's application, which works ok now.
Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

net/ipv6/addrconf.c

@@ -2281,6 +2281,9 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 				break;
 			}
 
+			if (!idev && dev->mtu >= IPV6_MIN_MTU)
+				idev = ipv6_add_dev(dev);
+
 			if (idev)
 				idev->if_flags |= IF_READY;
 		} else {
@@ -2345,12 +2348,18 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 		break;
 
 	case NETDEV_CHANGEMTU:
-		if ( idev && dev->mtu >= IPV6_MIN_MTU) {
+		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 (idev)
+				break;
+		}
+
 		/* MTU falled under IPV6_MIN_MTU. Stop IPv6 on this interface. */
 
 	case NETDEV_DOWN: