CVE-2026-74718: devlink: fix net namespace reference leak in reload

In the Linux kernel, the following vulnerability has been resolved:

devlink: fix net namespace reference leak in reload

devlinknlreloaddoit() calls devlinknetnsget(), which returns a net with a held reference. When the requested namespace differs from the current one and the reload action is not DRIVERREINIT, the function returns -EOPNOTSUPP without releasing the reference. Add the missing putnet() on this error path.