tcp: Fix double sizeof in new tcp_metrics code

Fix double sizeof when parsing IPv6 address from
user space because it breaks get/del by specific IPv6 address.

	Problem noticed by David Binderman:

https://bugzilla.kernel.org/show_bug.cgi?id=49171

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_metrics.c

@@ -864,7 +864,7 @@ static int parse_nl_addr(struct genl_info *info, struct inetpeer_addr *addr,
 	}
 	a = info->attrs[TCP_METRICS_ATTR_ADDR_IPV6];
 	if (a) {
-		if (nla_len(a) != sizeof(sizeof(struct in6_addr)))
+		if (nla_len(a) != sizeof(struct in6_addr))
 			return -EINVAL;
 		addr->family = AF_INET6;
 		memcpy(addr->addr.a6, nla_data(a), sizeof(addr->addr.a6));