mptcp: Fix TCP_FASTOPEN server-side processing

During the merge, I incorrectly set rcv_nxt again on the child-socket.
That's not needed, thus revert it again.

Fixes: c61bc63 ("Merge tag 'v4.15-rc3' into mptcp_trunk")
Signed-off-by: Christoph Paasch <cpaasch@apple.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>

net/ipv4/tcp_fastopen.c

@@ -275,8 +275,6 @@ static struct sock *tcp_fastopen_create_child(struct sock *sk,
 	/* Now finish processing the fastopen child socket. */
 	tcp_init_transfer(child, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB);
 
-	tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
-
 	/* tcp_conn_request() is sending the SYNACK,
 	 * and queues the child into listener accept queue.
 	 */