ipv6: tcp: give socket pointer to control skbs

tcp_v6_send_response() send orphaned 'control packets'.

These are RST packets and also ACK packets sent from TIME_WAIT.

Some eBPF programs would prefer to have a meaningful skb->sk
pointer as much as possible.

This means that TCP can now attach TIME_WAIT sockets to outgoing
skbs.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Brian Vazquez <brianvv@google.com>
Link: https://patch.msgid.link/20241010174817.1543642-5-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv6/tcp_ipv6.c

@@ -967,6 +967,9 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
 	}
 
 	if (sk) {
+		/* unconstify the socket only to attach it to buff with care. */
+		skb_set_owner_edemux(buff, (struct sock *)sk);
+
 		if (sk->sk_state == TCP_TIME_WAIT)
 			mark = inet_twsk(sk)->tw_mark;
 		else