net: Fix a data-race around sysctltstampallow_data.
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v4.9.327 by commit 64fca2207e068502dd2463ebb8d192083df1f4f8, it was introduced in version v4.0 by commit b245be1f4db1a0394e4b6eb66059814b46670ac3. For more details please see the references link.