netfilter: Use flowi4 and flowi6 in xt_TCPMSS

static u_int32_t tcpmss_reverse_mtu(const struct sk_buff *skb,

				    unsigned int family)

{

	struct flowi fl = {};

	struct flowi fl;

	const struct nf_afinfo *ai;

	struct rtable *rt = NULL;

	u_int32_t mtu     = ~0U;

	if (family == PF_INET)

		fl.fl4_dst = ip_hdr(skb)->saddr;

	else

		fl.fl6_dst = ipv6_hdr(skb)->saddr;

	if (family == PF_INET) {

		struct flowi4 *fl4 = &fl.u.ip4;

		memset(fl4, 0, sizeof(*fl4));

		fl4->daddr = ip_hdr(skb)->saddr;

	} else {

		struct flowi6 *fl6 = &fl.u.ip6;

		memset(fl6, 0, sizeof(*fl6));

		ipv6_addr_copy(&fl6->daddr, &ipv6_hdr(skb)->saddr);

	}

	rcu_read_lock();

	ai = nf_get_afinfo(family);

	if (ai != NULL)