ip/options: explicitly provide net ns to __ip_options_echo()

__ip_options_echo() uses the current network namespace, and
currently retrives it via skb->dst->dev.

This commit adds an explicit 'net' argument to __ip_options_echo()
and update all the call sites to provide it, usually via a simpler
sock_net().

After this change, __ip_options_echo() no more needs to access
skb->dst and we can drop a couple of hack to preserve such
info in the rx path.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/tcp.h b/include/net/tcp.h
index bb1881b..5173fec 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1885,7 +1885,8 @@ extern void tcp_rack_reo_timeout(struct sock *sk);
 /*
  * Save and compile IPv4 options, return a pointer to it
  */
-static inline struct ip_options_rcu *tcp_v4_save_options(struct sk_buff *skb)
+static inline struct ip_options_rcu *tcp_v4_save_options(struct net *net,
+							 struct sk_buff *skb)
 {
 	const struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt;
 	struct ip_options_rcu *dopt = NULL;
@@ -1894,7 +1895,7 @@ static inline struct ip_options_rcu *tcp_v4_save_options(struct sk_buff *skb)
 		int opt_size = sizeof(*dopt) + opt->optlen;
 
 		dopt = kmalloc(opt_size, GFP_ATOMIC);
-		if (dopt && __ip_options_echo(&dopt->opt, skb, opt)) {
+		if (dopt && __ip_options_echo(net, &dopt->opt, skb, opt)) {
 			kfree(dopt);
 			dopt = NULL;
 		}