tcp: Fix a data-race around sysctltcpmtuprobefloor.
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 v5.15.58 by commit cc36c37f5fe066c4708e623ead96dc8f57224bf5, it was introduced in version v5.4 by commit c04b79b6cfd714144f6a2cf359603d82ee631e62. For more details please see the references link.