net: tcp: fix crashes trying to free half-baked MTU probes

tcp_stream_alloc_skb() initializes the skb to use tcp_tsorted_anchor
which is a union with the destructor. We need to clean that
TCP-iness up before freeing.

Fixes: 736013292e3c ("tcp: let tcp_mtu_probe() build headless packets")
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20231010173651.3990234-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/tcp_output.c

@@ -2456,6 +2456,7 @@ static int tcp_mtu_probe(struct sock *sk)
 
 	/* build the payload, and be prepared to abort if this fails. */
 	if (tcp_clone_payload(sk, nskb, probe_size)) {
+		tcp_skb_tsorted_anchor_cleanup(nskb);
 		consume_skb(nskb);
 		return -1;
 	}