pidfs/selftests: ensure correct headers for ioctl handling

JIRA: https://issues.redhat.com/browse/RHEL-107520
Conflicts:
  A context diff due to missing upstream commit 59a42b0
  ("selftests/pidfd: add pidfs file handle selftests").

commit 18938f7
Author: Christian Brauner <brauner@kernel.org>
Date:   Wed, 5 Mar 2025 11:08:18 +0100

    pidfs/selftests: ensure correct headers for ioctl handling

    Ensure that necessary ioctl infrastructure is available.

    Link: https://lore.kernel.org/r/20250305-work-pidfs-kill_on_last_close-v3-8-c8c3d8361705@kernel.org
    Signed-off-by: Christian Brauner <brauner@kernel.org>

Signed-off-by: Waiman Long <longman@redhat.com>

Author: Waiman-Long

tools/testing/selftests/pidfd/pidfd_setns_test.c

@@ -16,7 +16,7 @@
 #include <unistd.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
-#include <linux/ioctl.h>
+#include <sys/ioctl.h>
 
 #include "pidfd.h"
 #include "../clone3/clone3_selftests.h"