kernel config: add CONFIG_IKHEADERS

BCC tools need to have access to kernel headers. It can be done either
by installing linux-headers packages or by having a kernel compiled with
CONFIG_IKHEADERS so that enough information can be retrieved via
/sys/kernel/kheaders.tar.xz.

BCC tools are used in Inspektor Gadget, a collection of tools for
developers of Kubernetes applications. I would like Inspektor Gadget to
support Minikube.

deploy/iso/minikube-iso/board/coreos/minikube/linux_defconfig

@@ -11,6 +11,7 @@ CONFIG_TASK_XACCT=y
 CONFIG_TASK_IO_ACCOUNTING=y
 CONFIG_IKCONFIG=y
 CONFIG_IKCONFIG_PROC=y
+CONFIG_IKHEADERS=y
 CONFIG_LOG_BUF_SHIFT=18
 CONFIG_CGROUPS=y
 CONFIG_MEMCG=y