ipv6: remove a useless NULL check

In dev_forward_change(), it is useless to check if idev->dev
is NULL, it is always non-NULL here.
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: NCong Wang <amwang@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -607,7 +607,7 @@ static void dev_forward_change(struct inet6_dev *idev)
 	dev = idev->dev;
 	if (idev->cnf.forwarding)
 		dev_disable_lro(dev);
-	if (dev && (dev->flags & IFF_MULTICAST)) {
+	if (dev->flags & IFF_MULTICAST) {
 		if (idev->cnf.forwarding)
 			ipv6_dev_mc_inc(dev, &in6addr_linklocal_allrouters);
 		else