netdevsim: set .owner to THIS_MODULE

netdevsim: set .owner to THIS_MODULE

If THIS_MODULE is not set, the module would be removed while debugfs is
being used.
It eventually makes kernel panic.

Fixes: 82c93a87bf8b ("netdevsim: implement couple of testing devlink health reporters")
Fixes: 424be63ad831 ("netdevsim: add UDP tunnel port offload support")
Fixes: 4418f862d675 ("netdevsim: implement support for devlink region and snapshots")
Fixes: d3cbb907ae57 ("netdevsim: add ACL trap reporting cookie as a metadata")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Link: https://lore.kernel.org/r/20201115103041.30701-1-ap420073@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>