tcp: Fix a data-race around sysctl_tcp_mtu_probe_floor.
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 v5.18.15 by commit e2ecbf3f0aa88277d43908c53b99399d55729ff9, it was introduced in version v5.4 by commit c04b79b6cfd714144f6a2cf359603d82ee631e62. For more details please see the references link.