x86: use kernel 6.18 by default

Switch to Linux kernel version 6.18.

Signed-off-by: Mieczyslaw Nalewaj <namiltd@yahoo.com>
Link: openwrt/openwrt#22893
Signed-off-by: Nick Hainke <vincent@systemli.org>

Author: namiltd

target/linux/x86/Makefile

@@ -10,8 +10,7 @@ BOARDNAME:=x86
 FEATURES:=squashfs ext4 vdi vmdk vhdx pcmcia targz fpu boot-part rootfs-part
 SUBTARGETS:=generic legacy geode 64
 
-KERNEL_PATCHVER:=6.12
-KERNEL_TESTING_PATCHVER:=6.18
+KERNEL_PATCHVER:=6.18
 
 KERNELNAME:=bzImage