net: call prot->release_cb() when processing backlog

__sk_flush_backlog() / sk_flush_backlog() are used
when TCP recvmsg()/sendmsg() process large chunks,
to not let packets in the backlog too long.

It makes sense to call tcp_release_cb() to also
process actions held in sk->sk_tsq_flags for smoother
scheduling.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/core/sock.c

@@ -3001,6 +3001,9 @@ void __sk_flush_backlog(struct sock *sk)
 {
 	spin_lock_bh(&sk->sk_lock.slock);
 	__release_sock(sk);
+
+	if (sk->sk_prot->release_cb)
+		sk->sk_prot->release_cb(sk);
 	spin_unlock_bh(&sk->sk_lock.slock);
 }
 EXPORT_SYMBOL_GPL(__sk_flush_backlog);