Kernel: T8871: Update Linux Kernel to 6.18.31

This fixes the LPE https://github.com/0xdeadbeefnetwork/ssh-keysign-pwn

Author: c-po

data/defaults.toml

@@ -14,7 +14,7 @@ vyos_mirror = "https://packages.vyos.net/repositories/current"
 vyos_branch = "current"
 release_train = "current"
 
-kernel_version = "6.18.29"
+kernel_version = "6.18.31"
 kernel_flavor = "vyos"
 bootloaders = "syslinux,grub-efi"