net: netdevsim: try to close UDP port harness races

syzbot discovered that we remove the debugfs files after we free
the netdev. Try to clean up the relevant dir while the device
is still around.

Reported-by:  <syzbot+2e5de9e3ab986b71d2bf@syzkaller.appspotmail.com>
Fixes: 424be63a ("netdevsim: add UDP tunnel port offload support")
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Link: https://patch.msgid.link/20250122224503.762705-1-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>