udp: use indirect call wrapper for data ready()

In most cases UDP sockets use the default data ready callback.
Leverage the indirect call wrapper for such callback to avoid an
indirect call in fastpath.

The above gives small but measurable performance gain under UDP flood.
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/d47d53e6f8ee7a11228ca2f025d6243cc04b77f3.1689691004.git.pabeni@redhat.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/udp.c

@@ -1553,7 +1553,7 @@ int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb)
 	spin_unlock(&list->lock);
 
 	if (!sock_flag(sk, SOCK_DEAD))
-		sk->sk_data_ready(sk);
+		INDIRECT_CALL_1(sk->sk_data_ready, sock_def_readable, sk);
 
 	busylock_release(busy);
 	return 0;