tcp: fix a panic on UP machines in reqsk_fastopen_remove

spin_is_locked() on a non !SMP build is kind of useless.

BUG_ON(!spin_is_locked(xx)) is guaranteed to crash.

Just remove this check in reqsk_fastopen_remove() as
the callers do hold the socket lock.

Reported-by: Ketan Kulkarni <ketkulka@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jerry Chu <hkchu@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Dave Taht <dave.taht@gmail.com>
Acked-by: H.K. Jerry Chu <hkchu@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/request_sock.c

@@ -186,8 +186,6 @@ void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
 	struct fastopen_queue *fastopenq =
 	    inet_csk(lsk)->icsk_accept_queue.fastopenq;
 
-	BUG_ON(!spin_is_locked(&sk->sk_lock.slock) && !sock_owned_by_user(sk));
-
 	tcp_sk(sk)->fastopen_rsk = NULL;
 	spin_lock_bh(&fastopenq->lock);
 	fastopenq->qlen--;