phonet: take correct lock to peek at the RX queue

The receive queue is protected by its embedded spin-lock, not the
socket lock, so we need the former lock here (and only that one).

Fixes: 107d0d9b8d9a ("Phonet: Phonet datagram transport protocol")
Reported-by: Luosili <[e-mail]>
Signed-off-by: Rémi Denis-Courmont <[e-mail]>
Reviewed-by: Eric Dumazet <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Paolo Abeni <[e-mail]>

net/phonet/datagram.c

···
 
 	switch (cmd) {
 	case SIOCINQ:
-		lock_sock(sk);
+		spin_lock_bh(&sk->sk_receive_queue.lock);
 		skb = skb_peek(&sk->sk_receive_queue);
 		*karg = skb ? skb->len : 0;
-		release_sock(sk);
+		spin_unlock_bh(&sk->sk_receive_queue.lock);
 		return 0;
 
 	case SIOCPNADDRESOURCE: