net: keep refcount warning in reqsk_free()

As Eric Dumazet said, "We do not have a way to tell if the req was ever
inserted in a hash table, so better play safe.".
Let's remove this comment, so that nobody will be tempted to drop the
WARN_ON_ONCE() line.
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/request_sock.h

@@ -108,7 +108,6 @@ reqsk_alloc(const struct request_sock_ops *ops, struct sock *sk_listener,
 
 static inline void reqsk_free(struct request_sock *req)
 {
-	/* temporary debugging */
 	WARN_ON_ONCE(refcount_read(&req->rsk_refcnt) != 0);
 
 	req->rsk_ops->destructor(req);