ipv6: Remove unused var in inet6_dump_ifinfo()

Reported by Stephen Rothwell:

--------------------
Today's linux-next build (x86_64 allmodconfig) produced this warning:

net/ipv6/addrconf.c: In function 'inet6_dump_ifinfo':
net/ipv6/addrconf.c:3833: warning: unused variable 'err'

Introduced by commit 84d2697d ("ipv6:
speedup inet6_dump_ifinfo()").
--------------------
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -3830,7 +3830,7 @@ static int inet6_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 {
 	struct net *net = sock_net(skb->sk);
 	int h, s_h;
-	int idx = 0, err, s_idx;
+	int idx = 0, s_idx;
 	struct net_device *dev;
 	struct inet6_dev *idev;
 	struct hlist_head *head;