bpf: Call maybe_wait_bpf_programs() only once from generic_map_delete_batch()

As stated in the comment found in maybe_wait_bpf_programs(),
the synchronize_rcu() barrier is only needed before returning
to userspace, not after each deletion in the batch.

Signed-off-by: Eric Dumazet <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Reviewed-by: Stanislav Fomichev <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

kernel/bpf/syscall.c

···
 		err = map->ops->map_delete_elem(map, key);
 		rcu_read_unlock();
 		bpf_enable_instrumentation();
-		maybe_wait_bpf_programs(map);
 		if (err)
 			break;
 		cond_resched();
···
 		err = -EFAULT;
 
 	kvfree(key);
+
+	maybe_wait_bpf_programs(map);
 	return err;
 }