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: 35e07d63aedd ("netdevsim: implement couple of testing devlink health reporters")
Fixes: 08cba40143b4 ("netdevsim: add UDP tunnel port offload support")
Fixes: e095a5a4a3b5 ("netdevsim: implement support for devlink region and snapshots")
Fixes: f4f1ce16d566 ("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>